Testing a battery...

[dougie]

My OEM BMW-Mareg battery is now 5 1/2 years old.
When I check it after a ride it shows about 13.5v - 13.7v.
About 24 hours later it reads about 12.5v- 12.7v, but of course there is the onboard clock running.
I tried a cold cranking test today. Grounded the plug wires but left the plugs in to maintain compression resistance. I ran the starter for about 15 seconds and the voltmeter never went below 10.8 volts. When I stopped, it went back up to 12.3 volts.
Is all this good or meaningless?
I would prefer to replace the battery before it lets me down, but don't want to waste a good year or 2 of use.

[Deleted User 72]

I know this is a trick question and I'm gonna get caught, bein' first. It sounds like a healthy battery to me, but I'm not personally acquainted.

[Major Softie]

Not even bothering with the voltage numbers, if you can crank the thing for 15 seconds with a 5-1/2 year-old battery, and it sounds healthy the whole 15 seconds (especially after sitting for 24 hours, then you have better luck with batteries than I do. If it can do that after sitting a week, then it's definitely in GREAT shape.

I would bet that thing has at least another year in it. If it can still do that a year from now, then probably 2.

[Garnet]

Don't you have a stock portfolio to worry about?

[Duane Ausherman]

MS is more correct than those voltage tests. If it cranks well, then that is all that you need to know. That doens't mean that it doesn't have any intermittent problems. The total capacity is greatly reduced by this time, but it isn't yet below being able to crank in a healthy manner.

I don't risk getting stuck, I replace them before they fail. It is time to replace it.

[Roy Gavin]

After over five years it isn't owe you much.

Like Duane I don't wait on batteries failing, as I don't like jump starting anything, or grinding the starter over when the battery has about 7 volts left in it.

IMHO the risk of damage to your starter, generator , diode board and regulator are not worth trying to squeeze another six months out of a $60- battery .

Motobatt batteries test well, but if you need the BMW size 51913/51814 or whatever 3'' wide, the Motobatt is 5mm bigger all round than some, and at 82 mm thick wont easily fit on a 3" carrier.

I just wasted the best part of a wet weekend making one fit my G/S - got it in there eventually but had to cut and modify the carrier and it is still too close for comfort to the top of the WP shock, and the air box.

[dougie]

Thanks folks.
Going to check on a Yuasa 53030.
Nice to know I can do it at my leisure, as long as it is before the COLD wearher sets in.

[Ken in Oklahoma]

IMHO the risk of damage to your starter, generator , diode board and regulator are not worth trying to squeeze another six months out of a $60- battery .

Roy, I'm having a hard time imagining how a "needs-to-be-replaced" battery can substantially increase the risk of damage to the parts you mentioned. At worst, it would appear to me, a battery at the end of its life will only require the ancillary electrical components to do a bit more of what they were designed to do, but nothing to my mind that would represent an extraordinarily shorter life span.

I'm not promoting prolonged use of a battery that needs replacement. The worry that the battery might fail me at a time when I really don't need that would alone be sufficient impetus for me to replace the battery. I just wouldn't be worried about the ancillary components until I did.


Ken

[Duane Ausherman]

"ancillary components" Ken, Diane likes it when you talk like that.

[Ken in Oklahoma]

"ancillary components" Ken, Diane likes it when you talk like that.

It's early in the morning and I'm fully caffinated. Tell her not to be expecting words like that all the time.


Ken, alert in Oklahoma