I think we can say that weight for weight, they are considerably better than NiCads.

We used to run three 24V packs of Sanyo 3Ah NiCads of THz, total weight around 5.7 kg. I dont think many people would consider running a heavy on just two packs.

We now run four packs of 34V A123s, total weight around 3.8 kg. So we have increased the voltage by almost 50% AND saved almost 2kg, with a similar capacity. That is a substantial improvement.

Even after a long hard fight, the A123s only get mildly warm - nowhere near 60 degrees. If your robot has a higher current draw, then you should use more packs (which you would need to do to have a safety margin on capacity) - theyll still be much lighter than NiCads.

Regarding cost, DeWalt battery packs see to be going for around £70 on ebay, so theyre cheaper than the equivalent amount of good NiCads too.

I didnt find them any more difficult to solder than NiCads, but adding the balance wires certainly is more work.

I believe they have now proven themselves and that the FRA should approve them for use ASAP.

Im not sure about approving all LifePO4 cells. I would imagine that there are some pretty ropey ones out there. The A123s are available at a reasonable price and perform well.

John