[dcat151]

A few months ago I replaced the stock battery in my 2006 Elise with a Braille B2015 and at the same time picked up a Griot's Garage Microprocessor-Controlled Battery Charger/Maintainer (this one: Battery Charger). The battery charger is supposed to charge the battery to 100% and then occasionally start an "exercise mode" where it puts a load on the battery, etc. to keep it maintained.

I set it on AGM 12v battery and 10a charging and this worked fine for the first few months, although every now and then I would check on the charger and it would show an error (in which case it stopped charging). According to the instructions, the error pops up when the battery's voltage doesn't rise as expected. In the past, I would just shut down the charger and restart it and there would be no issue (at least for a while). However, earlier this week I started getting an error every day (which means it stops charging when the error pops up). The error only shows up after the charger has charged the battery to 100% and is not yet in "rest" mode. (According to the instructions it is still working to get the battery to a "true" 100% charge, whatever that means.) The charger also shows the voltage of the battery while charging. I noticed that this week it's been getting up to 13.6, but then dropping back down to 12.8 or 12.9. (I believe I recall that in the past, the voltage during charging has risen as high as 14.4, but I could be remembering incorrectly.) I've checked the voltage with a voltmeter and it seems to square with the charger's reading.

So, here's my question: is it a bum battery or a bum charger? I've had no issues starting the car, even when it's been sitting out all day without a charger on it. For whatever reason, the charger doesn't think the voltage is getting high enough and shuts down. Should I replace the charger with a different type that won't shut down in this situation? I guess the battery could be bad, but it's only a few months old and has been kept on a charger since it was installed in the car.

 

[enderw88]

Take the battery to your FLAPS and get it checked out. If it is good, then the charger is the culprit...

 

[dcat151]

Thanks. Of course when I woke up this morning everything was working fine, so I'm leaning towards the charger. Either that or it's my fallback reason for weird things that happen to this car: "because it's a Lotus".

 

[enderw88]

Thanks. Of course when I woke up this morning everything was working fine, so I'm leaning towards the charger. Either that or it's my fallback reason for weird things that happen to this car: "because it's a Lotus".

That does add evidence against the charger, but the FLAPS tester can put the last nail in its coffin.

 

[DDJ74]

Resting charge is not that important. Anything over 12.5 is normal when car has been sitting. While running it should be around 13.5 to 14.4

Best way to test a battery is under load. If it cranks slowly is an easy sign of a bad battery.

Lastly how long does your car sit that you need a battery tender in Georgia? I just start my car once a week and let it run for a bit which is enough to keep the battery in good shape.

 

[dcat151]

I try to drive it at least weekly; it just depends on how the week goes. With it being a lightweight battery, I thought it better safe than sorry, so I hook it up to the charger. I think it probably couldn't go too much more than a week in between drives and still have a useful charge.

It's also been suggested that because it's a smaller battery the 2a charging setting might work better than the 10a setting. I'll give it a go and see what happens.

 

[oldmansan]

Resting charge is not that important. Anything over 12.5 is normal when car has been sitting. While running it should be around 13.5 to 14.4

Best way to test a battery is under load. If it cranks slowly is an easy sign of a bad battery.

Lastly how long does your car sit that you need a battery tender in Georgia? I just start my car once a week and let it run for a bit which is enough to keep the battery in good shape.

To clarify what I think he meant to say, the reading with no load is pretty much worthless. You can have 15 volts with little amperage and you won't won't crank the motor over. The charge under a load is what matters. Volts = pressure. Amperage = current.

San

 

[DDJ74]

To clarify what I think he meant to say, the reading with no load is pretty much worthless. You can have 15 volts with little amperage and you won't won't crank the motor over. The charge under a load is what matters. Volts = pressure. Amperage = current.

San

Thanks for making it more clear but yes that's basically what i was saying. A bad battery can have good volts but low amps. If the battery is weak in amps then voltage wouldn't matter. Battery at 12.5 with good amps will keep a stable voltage thus turn over quickly but a battery with low amps will cause a dip in voltage thus turn over slowly, barely or not at all. Battery tenders in my opinion are good if your not using the car at all for long periods such as winter storage. If you drive it once a week should be enough unless the battery is weak. Battery tender won't fix that though. Some good tips is not arming the alarm if its in your garage. Just lock the doors. Fully alarmed car will slowly drain battery power.