Flattened auxiliary battery - any consequences?

[NightPHEVer]

I recently managed to completely flatten my auxiliary battery (inadvertently left too much switched on while I was changing a flat tyre in 'challenging' circumstances, hey though at least I had a spare wheel and tyre! - see 'unequal tread depths' post). Even the hazards wouldn't work, just curiously the rear wiper, very slowly, even though it wasn't actually switched on at the time. Nice Mitsubishi breakdown man Adam jump started it, everything ok and auxiliary battery showing 100% condition on his measuring device. So are there likely to be any consequences of this battery flattening faux pas? DId this about three weeks ago and all seems ok - do these auxiliary batteries really cost £600? What type of battery is this? It's actually a bit bigger than it looks when you take the cover off. How long is one likely to last.

[Tipper]

Considering that these batteries take no heavy starting duty and their load is mainly lights and auxiliaries, plus the control systems of course, they actually seem a little under sized for their duty. I would have thought a higher Amphr capacity would have been needed but not one capable of providing high starting current. I've heard of several that have died but usually from leaving the auxiliaries on without the car being in 'ready' state which is when the battery is charged.

Quite why they are 'specified' so as to be so expensive seems odd considering their light duty. As it has no starting current needed I would think a 'leisure' battery would do the job nicely. I have seen a Yuasa battery being suggested as a replacement and even one from Halfords so I would tend to go with the correct Amphr size of whatever make I fancy and let the car deal with the charging needs.

[HHL]

Somewhere in the manual it states that the BMU will lose data (maybe reset), but that won't happen until it is disconnected for longer.
My friend did that for a few hours while installing a wiring for a transceiver and it seemed to have no ill effects.
As for pricing, after all it is supplied by the same people that can charge many hundreds for a key replacement without blushing.....

[Steeeeve]

'Somewhere in the manual it states that the BMU will lose data (maybe reset)' , little off topic but I wonder if this does reset the Bmu, I assumed the data was non-volatile. Question is, would there be any Ill effect from disconnecting the aux battery overnight and isolating the traction battery overnight to test.. Quite an intriguing idea

[HHL]

'Somewhere in the manual it states that the BMU will lose data (maybe reset)' , little off topic but I wonder if this does reset the Bmu, I assumed the data was non-volatile. Question is, would there be any Ill effect from disconnecting the aux battery overnight and isolating the traction battery overnight to test.. Quite an intriguing idea

Well, I believe the BMU does have a backup battery in it, but I don't know whether that just holds enough charge to enable the aux battery replacement without resetting it.
I did notice that my friend's SOH was quite a bit higher than mine last time we checked (about 6 months ago). That was some time after he had installed the radio and had the aux disconnected for nearly a day (incidentally, it seems impossible to find a place in the firewall to route another cable into the cabin).
At the time, his showed 96% and mine 90, from memory, and I was surprised as the cars were very close in built date and his had about twice as many km on it than mine.

[greendwarf]

'Somewhere in the manual it states that the BMU will lose data (maybe reset)' , little off topic but I wonder if this does reset the Bmu, I assumed the data was non-volatile. Question is, would there be any Ill effect from disconnecting the aux battery overnight and isolating the traction battery overnight to test.. Quite an intriguing idea

Well, I believe the BMU does have a backup battery in it, but I don't know whether that just holds enough charge to enable the aux battery replacement without resetting it.
I did notice that my friend's SOH was quite a bit higher than mine last time we checked (about 6 months ago). That was some time after he had installed the radio and had the aux disconnected for nearly a day (incidentally, it seems impossible to find a place in the firewall to route another cable into the cabin).
At the time, his showed 96% and mine 90, from memory, and I was surprised as the cars were very close in built date and his had about twice as many km on it than mine.

Perhaps that's all the dealer does in these semi-mythical BMU resets that result in apparent increased SoH - disconnect the aux battery overnight.

[MikkB]

INice Mitsubishi breakdown man Adam jump started it,

I wanted to ask if it was possible to jump start the PHEV, obviously it is. I have a little mobile jump start battery - out of interest, how should I go about jump starting the PHEV if I needed to? As I recall when the battery cover in the boot is opened only one terminal is exposed.

[Regulo]

There's a designated terminal in the engine bay fuse box for the purpose. See section 9 of the manual.

[MikkB]

Ah I see, thank you. That might be tricky with the very short cables that come with the compact jump starter I have, I guess I would need some sort of extender cable for at least one side. At least I now know which end of the car I should be at.. Cheers.

[Regulo]

You don't have to use the earthing point in the diagram. If you can find a nearer good earth, use that. It's probably recommended to use that one, to alleviate the risks of short circuits. I'd go out and have a look, but it's P'ing down here!