Lithium Battery Load Repair_ A Cost-effective Do-It-Your self Resolution for Your Workbench

Do you use battery-powered devices? By altering the cells in your item’s battery pack, it can conserve you cash money as well as downsize waste. Have a look at this do it yourself resolution.

It’s All Gone Silent…


ed devices operating Li-ion cells really keeps its effectiveness for a lot longer in contrast with the NiMH cell-based power tools of the previous. However, after lots of cost/discharge cycles, there comes a time when the vigor storage space capacity of also among the very best lithium battery goes down so reduced that the battery pack have to be altered. I have actually currently seen this with a great deal of my really own gizmos, as well as companions as well as coworkers generally turn to me for referral on this issue.

The only resolution is to visit the devices manufacturer’s website to see if a alternative battery pack is around. Generally there isn’t as well as, when there might be, the expenses can come as a shock. In my situation, the devices struggled merely reliable as well as concerned to have an exceptional couple of additional years of life in it — a brand-new battery would certainly be adequate. In such situations, it might be rewarding hacking the battery pack as well as altering the individual cells when the moment comes, which is generally less costly total amount. We will certainly also consider improving the effectiveness by altering the one-of-a-kind cells with a few of a much better requirements. When you in addition pick this course, you’ll wish to fireside up the welding torch together with bursting out the screwdrivers.

Hack a Battery Load?

It’s a well-recognized tale. After simply a couple of years of usage, the cordless screwdriver desires billing additional generally, as well as the cordless vacuum doesn’t have the vitality to gather your crumbs. In my case, it was the robotic lawnmower giving up the ghost mid-mow, stubbornly refusing to return to its charging station. The only and costliest resolution is to order a alternative battery pack. However have you ever thought of simply changing the cells within the battery pack? This strategy saves cash and reduces waste. Moreover, you possibly can choose alternative cells with a bigger capability than the originals. This isn’t only a restore; it’s an improve!In my case, I seen that my Robbi lawnmower solely needed to mow for half an hour earlier than it beetled off to its charging station for a 1.5-hour recharge.[1] Beforehand, the same old sample had been an hour of mowing adopted by a 1-hour recharge. Was this transformation in routine an indication? Having had Robbi for 4 years and figuring out it’s powered by lithium cells, it was clear that they’d doubtless want changing.Later that afternoon, I noticed it had been quiet exterior for a while. There, in the midst of the garden, Robbi had shut down and couldn’t be woken by urgent its buttons. I lugged it over to the charging station and put it on cost. Robbi finally sprang into life, and I learn from a menu possibility that its elapsed working time was 2,938 hours. Equivalent to nearly 1,500 cost cycles, it was clear that I ought to take into account sourcing a brand new battery quickly.‘Quickly’ got here sooner than anticipated. After its full cost, Robbi completed its work, however it didn’t get up the subsequent morning. Placing it on cost didn’t assist both. I had just lately handled the garden with some fertilizer, and we’ve got had numerous rain, so I wanted to behave rapidly. I may nearly hear the grass rising…

The producer’s alternative battery pack was priced at round €100, and a alternative from a third-party provider was obtainable for round half that worth, which isn’t that unhealthy. From its specification, I used to be in search of an 18 V alternative pack with a capability of two.1 Ah. That meant 5 cells, in all probability in the usual 18650 define. To verify my suspicions, I set about eradicating the lid of the battery compartment.

Unsurprisingly, this was simpler mentioned than completed. Three of the screws got here out simply, however the fourth was fully jammed. Finally, it got here out, however the captive mounting nut was ripped out within the course of, jammed on the screw thread. It regarded prefer it has been cross-threaded throughout meeting on the manufacturing unit. Determine 1a reveals the captive nut recess within the mower casing after removing. Some particles remained. I finally separated the screw and nut and, regardless of a part of the captive brass nut breaking off (Determine 1b), it regarded repairable.

Determine 1: One of many screws had been cross-threaded throughout meeting. It will definitely got here out however took the captive nut with it. It was repaired utilizing epoxy.

The battery compartment is designed to be waterproof, so the captive nut required remounting to make sure all 4 screws may very well be tightened for an excellent seal. I used an epoxy adhesive to safe the nut, and you may see the lead to Determine 2b. The brass nut on the high left appears as if it’s been there endlessly. With the mechanical half fastened, consideration turned to the battery pack. Determine 2b reveals the battery in its compartment. The define of 5 cells is clearly seen, and a ruler confirmed that they had been 18650 cells. There’s additionally lots of free house (Determine 2c), which received me considering: may I higher use the house by utilizing extra or bigger alternative cells? My thoughts wasnow made up: buying an off-the-shelf alternative battery was now not an possibility.

Determine 2: Battery compartment lid (2a), with the outdated battery in situ (2b) and the empty compartment (2c).

Battery Cell Swap

Determine 2a reveals that two recesses within the battery lid encroach into the obtainable battery house, ruling out the becoming of two rows of 5 cells to double capability. There are, nonetheless, dearer cells within the 18650 format with increased capability. A number of the better-known manufacturers have cells on this format with scores of as much as 3,500 mAh. Such high-capacity branded cells value an excellent 10 € every. You can too discover cells with a lot increased scores on eBay, AliExpress, and related websites, however you must take such claims with a pinch of salt.

I nearly positioned an order for 5 cells till I seen some others within the considerably extra uncommon 21700 format. Though solely barely bigger, they provided considerably extra capability for the cash. I used to be certain they would slot in someway (I used to be considering of a row of three and a row of two to type a W profile). With a amount low cost and postage, the 5 × 4,000 mAh cells got here to €26 in complete. They dropped by means of the letterbox two days later, and it wasn’t a day too quickly — the grass was now undoubtedly in want of a trim.


Constructing a battery pack from particular person cells usually requires a level of dexterity, electrical experience, and a spot welder. As you possibly can see from the outdated unwrapped battery pack in Determine 3, the 5 inexperienced cells are neatly related on the constructive and unfavorable contacts through skinny, spot-welded nickel strips. Such a everlasting connection technique does not injury the cell. Though the warmth generated throughout spot welding is intense, it’s swift and localized, so the cells are barely warmed. It’s well-known you possibly can by no means have too many instruments, however, on this situation, I can’t think about the place else I might use a spot welder, so I can’t justify the outlay. As a substitute, I selected to solder the wires on to the cell contacts. This isn’t really helpful except you observe some guidelines and are conscious of the hazards.

Determine 3: The outdated battery pack is wrapped in black gaffer tape (3a). The cells and BMS board are seen with the highest layer of tape eliminated (3b). A boxed and unboxed 21700 cell compared with the outdated 5-cell 18650 pack (3c).

The battery pack utilized in Determine 3 is typical of that discovered in lots of different battery-operated gadgets. It consists of a number of battery cells related in collection plus a Battery Administration System (BMS) PCB. That is the circuit board proven in Figures 3b and 3c. The latter picture additionally reveals a measurement comparability between the brand new cells and people within the outdated battery pack. The BMS performs three fundamental capabilities:

It balances the cells (i.e., retains all of them on the identical voltage or cost state). It prevents the cells from being overcharged. It disconnects the load within the occasion of undervoltage to keep away from deep discharge.

The chip on the BMS board with essentially the most legs manages all these duties. It’s a specialised microcontroller that displays the cell voltages (through the connector on the left). Within the occasion of an overvoltage or undervoltage situation, it disconnects the cells utilizing 2 × 2 MOSFETs (on the backside). Additional studying on balancing lithium batteries is out there below [2] and [3].

The BMS is included when you purchase a complete new battery pack meeting, so the BMS board (which nonetheless works) from the outdated pack can be redundant. However, when you solely swap the cells, you possibly can reuse the prevailing BMS board. An necessary characteristic of the BMS that you just want to concentrate on is described within the BMS Flip-Flop Perform part beneath.

BMS Flip-Flop Perform After I eliminated the battery proven in Determine 3c, I used to be shocked to measure 19.2 V straight on the plus and minus contacts of the 5-cell battery pack. Had I been too hasty in ordering replacements? However, I may solely measure about 18.5 V on the battery pack connector the place it connects to the mower motor (to the fitting of the BMS board), which had a really excessive supply impedance. Utilizing simply my fingers, I may discharge this to floor, inflicting the voltage to drop to only a few volts. Was the BMS damaged? I related a 24 Ω load resistor on to the cell contacts on the battery pack and measured a present of 0.75 A and a battery voltage of 18.2 V. I then disconnected the load and put the pack onto cost. After only a few seconds of charging at 0.5 A, the voltage output from the BMS switched to low impedance mode to attract some present from the battery through the BMS. It regarded just like the BMS had detected the battery voltage falling beneath the undervoltage threshold when the mower was final used and had turned off the FET to disconnect the battery. This ‘off’ state had been latched within the BMS. To check it, I related a 12 Ω load to the battery. After 5 minutes, the BMS switched off at simply over 13 V and switched on once more after one other cost. Phew… With the BMS good to go, I proceeded with the cell swap.

Hold Soldering On

With no spot welder handy, I made a decision to solder stranded wire on to the battery terminals. So long as you’re cautious, this may be completed with out harming the batteries. Any thermal injury inflicted on the constituent supplies of the cells is roughly proportional to the integral of time and temperature. In different phrases, you must be fast! Three issues are necessary right here. Firstly, the soldering iron should be highly effective sufficient for the tip to take care of its temperature throughout soldering. This ensures that the top of the cell rapidly achieves soldering temperature. A solder that melts at a decrease temperature can be advisable. I used a 90 W iron because it has a regulator that permits the bit temperature to be set at over 400°C. It’s best to keep away from lead-free solder for this job because it melts at a better temperature and doesn’t moist the floor as properly as the nice outdated SnPb 60/40 that I choose. In my expertise, the steel contact surfaces of the lithium cells take the solder simply. With the tip temperature set to 385°C and utilizing 1 mm diameter, flux-cored solder, I accomplished every joint in round one second — quick sufficient to keep away from damaging the cell.

If you must preserve the soldering tip on the cell contacts for for much longer than this (as a result of the soldering iron is underpowered, the temperature is simply too low, or by means of the usage of lead-free solder), you threat overheating and damaging the cell. This can affect the cell’s electrical capability and presumably scale back the variety of cost/discharge cycles. So long as the iron is simply in touch with the floor for round a second, it shouldn’t trigger any hurt. Alternatively, you could possibly purchase some barely dearer tagged cells that include a brief nickel strip already spot welded onto the cell contacts. The strips can then be soldered collectively to make up the pack with none threat of overheating the cell contents. In precept, that is safer, however you have to insulate the naked strips to forestall any brief circuit. A brief circuit throughout regular operation will create a considerably extra harmful situation than may happen by making use of a brief blast of warmth to solder wires to the cell contacts.

A detailed-up of my soldering technique will be seen in Determine 4. The constructive contact consists of a steel cap hooked up to the battery electrode at three factors on this cell. This association will increase the thermal resistance between the skin contact floor and the cell’s inside construction, making it extra tolerant of the soldering course of. Begin by making use of small drops of solder to tin all of the constructive contacts (Determine 4a) rapidly. Subsequent, lower 1.5 mm2 stranded wire to a size of three cm, which permits some leeway for later positioning of the cells within the pack. These can now be soldered straight onto the unfavorable contacts (Determine 4b) in two levels. Firstly, use the soldering iron and solder them rapidly to determine a small tinned space within the heart of the contacts. Subsequent, strip and tin the ends of the connecting wires. As soon as the cells have cooled, rapidly solder a wire to every of the unfavorable contacts. In Determine 4c, you possibly can see the opposite finish of a wire now soldered to the constructive contact of the subsequent cell to make the collection connection. The thinner pink wire is the cell voltage sense connection to the BMS board.

Determine 4: The constructive contact is extra tolerant of the soldering process (4a). Quick lengths of wire are soldered to the unfavorable contact (4b). The cells are lastly related in collection, and the thinner voltage sense wires are related to the BMS (4c).

Assemble and Check

As already talked about, the battery compartment can not accommodate the 5 cells organized in rows of two and three to type a W configuration, so I needed to discover a totally different pack building. In Determine 5, you possibly can see that 4 of the cells are positioned subsequent to at least one different and stuck in place with sizzling glue. The fifth cell is glued throughout the opposite 4. The recent glue makes the completed meeting very steady. You would alternatively use silicone sealant right here.

Determine 5: Underside of the completed pack (5a) and high view with the BMS board (5b).

The double-sided tape on the again of the BMS board didn’t should be changed because it held firmly to the brand new battery pack. All that remained was to attach the six wires from the white connector (Determine 5b) to the corresponding cell contacts, together with the plus and minus connections of the complete pack, to the BMS board. This should be accomplished earlier than we will check the brand new battery. Double-check all of the wiring to make sure you haven’t made any errors. Taking a photograph of the outdated battery pack will assist at this later stage when checking the whole lot. The battery pack functioned as anticipated and may very well be charged and discharged and not using a downside.

The completed battery pack was wrapped in gaffer tape to make the meeting extra sturdy and supply insulation and moisture ingress safety (Determine 6) earlier than becoming into the mower’s battery compartment. After screwing down the lid and switching on the mower, it needed to calibrate itself with the sign from the information cable and to start out mowing instantly. I canceled the latter operation and put it into its charging station. It wanted a full three hours to cost, indicating that the battery now has nearly twice the capability of the unique.

Determine 6: The brand new pack wrapped in orange gaffer tape (6a) matches neatly within the housing (6b).

The robot mows in addition to it ever has — an hour of mowing adopted by an hour of billing. The battery is simply partially discharged throughout these cycles, so I assume that these bigger capability cells will tolerate considerably extra charging cycles earlier than they want changing once more. Hopefully, I reckon the brand new pack ought to final twice so long as the unique. If that’s the case, the trouble concerned in three hours of tinkering was in all probability worthwhile. Figuring out the hourly wage fee for the time taken, the fiscal side appears poor, however, on the plus aspect, I now have an answer that may’t be purchased off the shelf.

This technique of battery cell alternative isn’t restricted to lawnmowers. You should use the identical strategy to increase the lifetime of cordless vacuum cleaners as well as different gadgets, even when the obtainable battery house is much less beneficiant. The final vacuum cleaner I repaired utilizing the tactic (utilizing high-capacity 18650 cells) has been in use for 3 years with none efficiency complaints.

Questions or Feedback?

Do you have obtained any technical questions or feedback regarding this message? E mail the Elektor staff at