For some time now, my Roomba has been wheezing and failing to complete it’s cleaning cycle. At first, it repeatedly failed to return to it’s base station, having gone low on power before it could do so. However, the deterioration progressed quickly, down from the normal 1 hour run time to 30 minutes, 15 minutes and finally, 5 minutes.
I guessed it’s time to replace the battery pack. But before I went ahead and put down some serious cash, I did a detailed search online and found some tips. It is possible that I could “refresh” the battery by reseting the Roomba, and forced it to re-learn the battery capacity. Apparently, the Roomba’s battery controller algorithm might no be as robust as it should be. Over time, it could accumulate error and flagged a good battery as running out of juice.
And so, I followed the tip on reseting the Roomba, get it to recharge the battery again; then, clocked the cleaning cycle time. I repeated this a few times over the course of two weeks, but in the end, the run time was still around 5 minutes. No luck.
Instead of purchasing a replacement battery from the local dealer (where I originally bought my Roomba), I decide to shop at Amazon.com. There were a couple of hits. A direct replacement Roomba APS battery cost USD59.95. However, I found an alternative third party supplier, Tenergy battery selling at USD26.99. That’s 50% saving! One catch though: the alternative battery was “raw” battery cells, minus the yellow plastic case. What this meant was that I would have to crack open the existing (depleted) battery, and replace the innards. Would it be an easy task? If the case got damaged in the process, then it’s going to cost more overall. But I decided it’s worth the risk.
Incidentally, the US postal did not ship Lithium Ion battery. The shipping option for the part was either “standard” or “express” (no explanation what they really meant). In line with “as cheap as possible” philosophy, I opted for “standard” shipping. The order confirmation stated about three weeks delivery time, and the shipping was a whopping 1.5 times the cost of the battery itself.
Surprisingly a week later, the order arrived via UPS. That made me felt less cheated about the high shipping cost. 
Removing the screws from the battery case
Taking out the battery from the bottom of the Roomba, I noticed eight screws to be removed. On closer examination, I noticed the screws were weird and extremely uncommon “triangle recessed” type.
Where was I going to find the tool to remove that? Thankfully, Tenergy has anticipated this problem. The battery shipment included the specific screwdriver to deal with it. Now, that’s smart!
One caution when removing the screws. One of the eight screws was shorter that the rest. This screw came from the leftmost side of the battery (above the battery terminals). Remember to put it back in the correct location later.
Cracking the battery case
After removing screws came the hard part. Unfortunately, the case cover was glued in. You would have to carefully pry on the seams, all the while avoiding piercing the battery cells inside (to prevent a toxic accident).
It took a fair amount of brute force (and cursing), but I finally broke the glue contact and pried the cover off.
Replacing the battery cells
After removing the existing battery cells from the case, I took a picture of the terminals, to ensure I do not messed up the wiring arrangement when doing the swapping.
The old (top) vs new (below) battery cells.
Next, de-soldered the battery terminals off from the old cells, and soldered them on to the new cells.
The new cells came with long wires, which needed to be cut to correct length before soldering on to the terminals. The new cells fit quite tightly into the case, and there was little room for slack in the wires’ length; so they needed to be quite exact. I slid the new cells into the case first, before cutting and soldering the wires on to the terminals.
Another thing to be careful about: do not allow any of the wires to come into electrical contact with each other. You might inadvertently damage the battery if you do so, or severely reduced it’s lifespan.
Final results
I left the Roomba to charge up with the new battery overnight. The first clean cycle with the new battery was 70 minutes. Success!
I am now reapplying the battery reset procedure and will clock the clean cycle time again after that.
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Comments 2
Great article but now you can purchase them already assembled (just drop it in) for 27.50 on ebay or about 37 on amazon, both including shipping.
Posted 27 Jul 2009 at 12:32 am ¶hi Charles
Thanks for the heads up. Indeed the prices for fully assembled Roomba batteries at Amazon has come down now. And if I need a new one, I would opt for those, rather than having to jury rig the Tenergy one.
As for free shipping, I probably don’t qualify (being outside the USA region).
Posted 27 Jul 2009 at 1:12 am ¶Post a Comment