I had described how to upgrade the firmware in the GigaPan Epic Pro to the latest (and last version). I also mentioned that it may be necessary to rebuild the battery packs at some point. This post describes the process of rebuilding the battery pack for the Epic Pro.

Note: Working on charged Nimh battery packs can be dangerous and/or hazardous. Do not attempt any work on a battery pack unless you understand how to work safely and have training and experience.

One of the two OEM battery packs had failed. The “fully charged” terminal voltage was 6.8 vdc and it had very low amp-hour capacity. This indicted that at least one cell had failed.

The first step in the rebuild was to open up the OEM pack:

This was accomplished by carefully cutting the outer shell along the obvious seem with a sharp utility knife and carefully using spudgers to pry open the case.

It turned out that one cell in the pack was completely dead (basically forming a resistor) and the rest had low terminal voltage. Several were visibly bulged. This pack was purchased with the EPIC Pro in 2013.

The next step was choose a replacement battery pack to test. As this was an experiment, I wanted to keep the cost reasonable. It turns out that 7.2 v Nimh battery packs for RC models are a close fit. I purchased an inexpensive 7.2v Nimh battery pack on with an advertised capacity of 3800 mAh. The OEM packs were rated at 4200 mAh. I knew in advance that the ratings of the cheaper battery packs were exaggerated significantly. In fact, I measured the capacity of the new pack at 1800 mAh. The replacement packed weighed about 298g and the OEM pack weighed 437g. This is a clear indication of the true capacity of the replacement vs original pack.

The replacement pack fit into the original case with no obvious issues*.

Next, I had to remove the existing wires and attached the original PPTC fuse and connector so that I could use the EPIC Pro charger.

I de-soldered the wires from the replacement battery pack and carefully removed the welded nickel tabs from the old battery pack.

Then I fitted the replacement pack into the original case. I had to remove one small section of the outer plastic shrink tube on the replacement pack in order to do this.

I used a couple of dabs of electronic grade (neutral cure) silicone to secure the replacement pack in the case. Then I carefully closed the case and used glued it at 6 points around the perimeter. I clamped the case shut while the superglue was curing to maintain the original dimensions (very important) of the case.

I tested the replacement pack by completed several charge/discharge cycles using the ORM EPIC Pro charged and my electronic load. I set up the load for 0.2C discharge rate which turned out to be 360mA. This resulted in a capacity of 1800 mAh.

The replacement pack fit into the EPIC Pro battery compartment with some friction at the pull-tab/locking end. *In hindsight I should have removed both ends of the shrink wrap on the replacement pack, which would have resulted in a better fit. But the pack is certainly usable as is.

Powering up the EPIC Pro with the replacement battery pack showed the battery at 100% capacity. I will do some field testing of the system in the near future, but I feel this has been a successful rebuild of the battery pack for the GigaPan Epic Pro.