Questions about the battery and charging system

7792 Views 23 Replies 10 Participants Last post by lordofthewings, Nov 11, 2016

iamz

Discussion Starter · Nov 2, 2016

Has anyone else been monitoring the battery voltage of their car while running? I'm noticing that at idle I measure only around 12.6 volts right after starting. And after cruising even 20 miles or so at highway speeds of 60 mph, I almost never see even 13 volts. After driving 40 miles today, all on the highway, it finally was showing around 13.2 volts of charging. Don't these numbers seem really low? I'm expecting to see upper 13's and above 14 some of the time, but have never seen even close to that.

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iamz

Discussion Starter · #3 · Nov 2, 2016

I got it figured out - I put the battery on a 6 amp charger last night and found it was taking a charge readily (a full 4 amps of draw for the first 5 minutes or so). After 15 minutes on 6 amps I dropped it down to 2 amps and left it on for another 45 minutes until the battery was drawing almost no amps. Today on the way in the car was now showing above 14 volts 90% of the time.

Apparently my car was delivered with a partially discharged battery. Keep in mind, with the engine off and no load, I was still getting a reading of 12.8 volts even though the battery was clearly not fully charged.

This might be something you guys might want to check on your cars. Add this to the "Pre-Delivery Check List".

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iamz

Discussion Starter · #6 · Nov 2, 2016

PureAdrenaline said:
This is normal for new technology charging systems. They essentially turn the alternator off for periods of time when the battery is fully charged and run off of the battery alone. This removes parasitic losses and saves fuel. Don't be surprised to see 12.0 readings.

I'll see what happens over the rest of the week of driving. I put on about 90 miles a day, so by Friday I'll know if it is going to stay where it's now at, or start to drop back down.

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iamz

Discussion Starter · #7 · Nov 2, 2016

MotoPete said:
The tread relates to NC's, but it would seem low 13's are the norm:

http://forum.miata.net/vb/archive/index.php/t-385233.html

I wonder how different the NC charging system is from the ND.

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iamz

Discussion Starter · #8 · Nov 6, 2016

Today I measured my battery voltage at 12.45 which means it is roughly at 75% of a full charge. Either I have a faulty battery or something is wrong with my cars charging system. I checked the acid level in all the cells and it's above the plates. I'm going to order a hygrometer and check specific gravity of all the cells next. I have a 50 minute, all highway commute to and from work every day so it should be getting a full charge.

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iamz

Discussion Starter · #10 · Nov 6, 2016

Everything I'm reading though says a healthy wet cell should read 12.6 minimum and AGM and gel cells should be around 12.85 at a full charge. All my motorcycles have AGMs and they are usually right around 12.75 to 12.85. If anyone else with a voltmeter could check their batteries that would help a lot.

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iamz

Discussion Starter · #12 · Nov 6, 2016

TomM said:
If you're convinced you have a problem, take it in somewhere and get it looked at. No point in fussing about it.

I'm trying to figure out if there is a problem. If there is a problem, I'll bring it in.

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iamz

Discussion Starter · #14 · Nov 8, 2016

Unknownsir said:
The dealership I am sure would test if u asked. But if not convenient, Around here there is an aftermarket parts house(advanced auto) that will do an in car battery test at no charge, I am not sure if places like NTB or sears or something might do it free too.

Yeah, I'll need to do a load test on it at some point. For now I'm just going to monitor it for awhile. I've got it charged up again and so starting tomorrow, I'll check the voltage at the end of each day and see if it keeps dropping. If it does keep dropping and the specific gravity of each cell measures good, I'll have it tested. If it tests good, then there is something wrong with the cars charging system. At that point I'll head in to the dealer.

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iamz

Discussion Starter · #17 · Nov 8, 2016

lordofthewings said:
During our forthcoming winter there may be periods of 2 weeks at a time when I don't drive the car, and I don't want a flat battery. Does anyone have experience of using a trickle charger that plugs into the 12v outlet (what would normally be the cigarette lighter socket) ? I've seen the results of a battery being overcharged and blowing a cell, not a pretty sight.

I'm ordering a Battery Tender Plus - you can find them on ebay for $44 delivered. That's for the bigger, non-California version with a 10 year warranty.