[paulgato]

I just spoke to a technical guy at Enersys in the UK about their Odyssey car batteries.

A longish and useful conversation in many ways, and he was interested enough in the fuel-saving project to take some time over the issue.

(This is often the case in my experience. These deeply knowledgable technical guys sit there all day answering the same old questions from non-techies about standard applications, and when someone has an interesting and novel application for a product they will often take a real interest and put their best thinking cap on to come up with a solution. I love engineers!)

It turns out that no, there is no metal jacket available for the PC1220 battery I wanted to use, and yes, without a metal jacket the maximum ambient temperature for the battery is 40 degrees C, whereas with a metal jacket the Odyssey batteries can operate at 80 degrees C.

But the "Aha!" moment came when he explained why. The metal jacket is NOT a heatshield. It is a mechanical restraint which prevents the battery physically expanding or 'ballooning' when the plastic casing heats up. When that happens the battery plates start to separate and the battery fails. These batteries can cope with high temperatures as long as they are mechanically reinforced.

So, we've been talking/thinking about heat shields and insulation, and that may help to some extent, but the main thing is to physically reinforce the battery casing, especially at the ends. I said to the guy, "So, if I were to put a square aluminium plate at each end of the battery and wrap glass fibre and resin around the whole thing, then that might do the job...?" He said, "That would do it."