I am now seriously thinking about converting the ALTAIR robots over to LiFePO4 (Lithium polymer) batteries they are expensive but the advantages are so great that I just have to do the conversion!
LiFePO4 are far safer that LiPo and less prone to catching fire, they also last for many more charging cycles before wearing out (up to 10 times as many!) other advantages
Less that 1/4 of the weight and a 1/3 of the size of lead acid batteries.
3 hour charge time.
Over 5 year shelf life
This is the batt pack and charger that would be a great fit for the ALTAIR's - 12volt 16Ah and it only weights 2.2kg!http://www.amazon.co.uk/LITHIUM-TROLLEY-POWAKADDY-HILLBILLY-REPLACES/dp/B00J4S1EQI
I am going to have to rebuild the locomotion bases to now house this battery, but it is well worth it!