NiMH Rechargeable Battery: 12 V 2200mAh (2x5S/S, MH-AA2200B) with Thermistor

Two years ago I bought a very similar battery from BatterySpace (the only difference is it was then rated for 2000mAh, not 2200mAh) for use in my bike's running light system. I've been using these for a couple years now and they're working out great. I have four Piranha automotive LED side marker lights on my bike: an amber one on each fork leg, and a red one on each seatstay. Each of these is about 2" long, contains two emitters, is very bright and consumes around 1/2 watt. I have four more of these units (in addition to $20 worth of DOT reflective tape) on my child's Chariot Sidecarrier trailer, with connectors that let me tap the trailer into the bike's running lights whenever I'm using it. Driven by a little 2000mAh 12V pack from batteryspace that I've had for a couple of years (current model is 2200mAh), I get 8-10 hours per charge running only the bike's running lights (more than enough for a week of commuting), or 4-5 hours with the trailer hooked up. This battery pack is tiny (300g), housed in a little canvas pack that I strap to the bike, and has performed flawlessly for nearly 2 years of year-round (yes, including summer) commuting. I'm not using a switch, since that's been a failure point for me in the past: I just plug the running lights in at the beginning of a ride, and unplug them at my destination. Approximate cost to build: $100. $30 for bike LEDs, $30 for trailer LEDs, $20 for battery, $20 for connectors and supplies. This assumes you already have a charger.