Too smart charger?

[RizzoTheRat]

For various reasons my bike's been sat in the work bike shed since Autumn, and stupidly I didn't get round to topping the battery up until today.

I plugged my CTEK MXS 5.0 in to it and a couple of minutes later it switched to power save mode which apparently it does if it's not connected to a battery. So it seems the battery is so knackered it's not even recognising.

The battery was new last year so that seems like a waste of money, but is it worth trying a dumb charger to get a bit of charge in to it so the CTEK recognises it and see if it manages to put enough charge in for me to take it home?

[mikey_b]

Might work. I have a couple of home battery chargers (like AA battery size), one smart the other more brutal. It’s often the case that a well discharged battery is ignored by the smart charger, but 10 seconds on the dumb charger wakes it up enough that the smart charger then recognises it fine.

[OutInTheShed]

Yes.
Also try connecting the Ctek and cycling the power, it may fool itself into working as it wakes up.

But if your battery is near dead, you might do well to replace it rather than give the starter motor a hard life.

[RizzoTheRat]

Tried cycling the power a few times and different modes to no avail. I have a dumb charger I could try on it, but wondering if it's just easier to bite the bullet and get another new battery, it's reasonably easy to access so probably doable to change it in the work carpark but it would be nice to be able get it home to do it.

[stang65]

Connect another battery as well for an hour or so. The charger will start charging then, and if the battery takes any charge it'll carry on when you disconnect the other battery. Worked for me in the past.

[OutInTheShed]

I've got loads of power supplies kicking about, so I'd just give it something like 14.5 to 15V current limited to a couple of amps for a few minutes and see if it still looks like a battery. I'm hesitant to advise people to try stuff they might cock up.

If the battery is still in circuit, you could be abusing the ECU, or there might be enough load that a trickle charger can't re-float the battery.

One trick is to use a notionally 12V supply like a wall wart and put a 12V 5W bulb in series. That will limit the current and slowly drag the battery up, to the point where the Ctek will see it as a battery.

At the end of the day, if the battery has been below about 8V for more than a week or two, chances are it's dead.
It's one thing to totally flatten a battery, you can get away with that if you recharge it within a few hours.

But you may be lucky.

FTAOD it is Lead Acid not lithium or anything?

[RizzoTheRat]

Yeah it's a gell one rather than lithium. Still on the bike but presumably won't case any issues to the electrics so long as I don't put too high a voltage on it.

My basic Halfords charger has a bike mode so I'll give that a try for a bit tomorrow and see what happens.

[OutInTheShed]

stang65 said:

Connect another battery as well for an hour or so. The charger will start charging then, and if the battery takes any charge it'll carry on when you disconnect the other battery. Worked for me in the past.

You can do that.
You might put a fuse between the two batteries or maybe an ammeter?
Remote chance the duff battery has shorted cells and it could all get a bit warm.

Might be unlikely, but if anyone gives advice often enough on the interweb, sooner or later 'unlikely' bites someone's arse.

[catso]

stang65 said:

Connect another battery as well for an hour or so. The charger will start charging then, and if the battery takes any charge it'll carry on when you disconnect the other battery. Worked for me in the past.

I did this to the battery from an old electric golf trolley.

CTEX wouldn't even see it as it was totally flat after being stood for a few years but doing it this way brought it back to life, of course it wasn't perfect/like new but it was good enough to get the motor tested and running again.