Each pack is 5 C cells. The attached leads are too thin [22 gauge] for this application, but there are ribbons spot welded to the cells and two ribbons that seem to have been test tabs. I used these ribbons and 14 gauge wire to interconnect the battery packs. I wired up two 24V 4AH strings. Each goes through a 20A fuse and to a SPDT switch. When switched on the strings are in parallel and when off they are seperate. I used an female XLR connector for charging, like the stock Currie box. I made a light, compact box out of 1/4" plywood with lots of metal 'L' brackets for bracing. The bottom is perforated board for a little ventilation.

After assembly I charged the batteries with a dual bench power supply. I charged them at 2A keeping a close watch [battery box open] until they started to feel warm. That took about an hour, so they came with a substantial charge. Then I charged them about 12 hours [overnight] at 200mA. They were then lukewarm and floating at about 28.5V.

I then mounted the box on the bike and took a test ride. First, going down [and later up] the stairs on the front of my house was less of a chore. My bat box is narrower than the Currie so it doesn't brush against my legs. Steering is more nimble.

On the down side there is slightly less low speed torque and I will have to work harder up steep hills. I rode about 6 miles without charging the pack and the power output was consistent. I wanted to run the batteries down to the low voltage cutoff [to break them in] but I decided to test the charger I built. The resting voltage was down to 24.8V but the motor seemed to pull as strongly as when freshly charged.

The charger I built is a simple affair. It delivers approx 2A to each string until a threshold voltage is reached, then it trickles at 100mA [C/40]. The trick is to set the threshold voltage low enough that the charge voltage never approaches the peak and fallback characteristic if nickel based batteries as the battery nears full charge, and that if a fully charged battery is connected it trips the threshold. With close observation I'll find a conservative threshold. Keeping ambient temp in a fairly narrow range helps to. Looks like 28.25V is about right. I know there are sophisticated battery management chips etc., but I built this baby from parts already on my shelf in a short time. It's trickling as I write. I chose a low trickle of 100mA to limit heating because of the tight packaging.