Could my battery be bad

[vikingknut]

When I received my AR250, I noticed my house battery was only at 11.7 volts. I only took it out once before upgrading the speakers, amplifiers (800x1 watt) and subwoofer. The first time I took it out after the upgrade, it was fine the first half hour or so, and then the volts dropped precipitously down to I believe 7.5. The stereo/amp stopped working, but the connext screen, etc was fine. I charged the battery for a little less than an hour (10 amp charger). When I took it out again, it was at 11.5 volts to start. Ran fine for 15-20 mins and then dropped again. 1. could the battery be bad? 2. Do I need a new deep cycle battery (AGM?)? 3. Could there be something wrong with my amp/setup? I was meticulous in wiring. I have the positive going to a 125 amp breaker/fuse and then to the house switch and the negative directly to the house battery negative.

 

[TommyMcK]

If your battery was discharged to the point that it was reading 7.5V, it was mostly discharged. Your 10A charger running for an hour puts way best case 10 amp-hours into the thing...so it was still possibly very under charged. You might consider fully charging the battery (simply looking at the output voltage won't tell you if it's fully charged.)

 

[lazergeek]

If your battery got o 7.5 volts its most likley damaged and will not get a full capacity again from it. Even if it takes a full charge I would not trust it. Lead acid batteries start getting damaged below 11.9v.

 

[Cobra Jet Steering LLC]

be sure the cables are connected properly , a loose connection to the battery will do that

 

[TommyMcK]

If your battery got o 7.5 volts its most likley damaged and will not get a full capacity again from it. Even if it takes a full charge I would not trust it. Lead acid batteries start getting damaged below 11.9v.

It's true that if you regularly subject a lead acid battery to over 50% depth of discharge it will damage the battery, and it's also true that the open circuit voltage should be over 12V at 50%, if you are relying on your boat display to show the battery charge, it isn't open circuit at that point. You are drawing from the battery at that point. It is very common under those circumstances to show less than 12V and that by itself doesn't indicate a bad battery. 7.5V is very low though and may in fact indicate that the depth of discharge was big enough to have taken a bite out of the battery's life.

 

[FSH 210 Sport]

When I received my AR250, I noticed my house battery was only at 11.7 volts. I only took it out once before upgrading the speakers, amplifiers (800x1 watt) and subwoofer. The first time I took it out after the upgrade, it was fine the first half hour or so, and then the volts dropped precipitously down to I believe 7.5. The stereo/amp stopped working, but the connext screen, etc was fine. I charged the battery for a little less than an hour (10 amp charger). When I took it out again, it was at 11.5 volts to start. Ran fine for 15-20 mins and then dropped again. 1. could the battery be bad? 2. Do I need a new deep cycle battery (AGM?)? 3. Could there be something wrong with my amp/setup? I was meticulous in wiring. I have the positive going to a 125 amp breaker/fuse and then to the house switch and the negative directly to the house battery negative.

11.7 volts? Was that on the connext?

With readings as low as 7.5 volts a flooded lead acid battery is in bad shape. Even If you did a full on manual equalizing charge the battery is on its way, not a good way to start the season.

Go get a new house battery. Go get an Interstate, Duralast or other flooded lead acid battery to replace it with.

Install a quality onboard charger with at least 10 amps of charging per bank, NOCO and MinnKota make good ones-don’t go cheap here and buy some off brand pos because it’s cheaper. Both of those chargers have manual equalizing charge cycles you can run, run an equalizing charge at least once a month during the season. Check the battery with a hydrometer.

Every time you come home from using the boat put it in the charger and leave it plugged in.

 

[TommyMcK]

11.7 volts? Was that on the connext?

With readings as low as 7.5 volts a flooded lead acid battery is in bad shape. Even If you did a full on manual equalizing charge the battery is on its way, not a good way to start the season.

Go get a new house battery. Go get an Interstate, Duralast or other flooded lead acid battery to replace it with.

Install a quality onboard charger with at least 10 amps of charging per bank, NOCO and MinnKota make good ones-don’t go cheap here and buy some off brand pos because it’s cheaper. Both of those chargers have manual equalizing charge cycles you can run, run an equalizing charge at least once a month during the season. Check the battery with a hydrometer.

Every time you come home from using the boat put it in the charger and leave it plugged in.

That's all great advice for sure...

The way I read his post though, it sounds like he started out with a house battery of unknown state of charge, went out, shut down someplace and ran an 800W stereo for a half-hour. I'm no stereo guru, but I think that the 800W rating is the power delivered out of the final output stage to the speakers, and the amp certainly won't be 100% efficient. But order of magnitude anyway has him in the (800/12)*0.5 = ~30amp-hour range if I'm doing the math right. If the battery was already not fully charged, it isn't necessarily surprising that the battery was struggling.

The 11.7V on the connext isn't particularly informative since the battery is under load but not under charge at that point (blower may have even been on).

The battery likely did have a good portion of its life consumed based on the description, and it's a good idea to replace it...but it sounds to me anyway based on the OP's description, he may need to consider how much he is drawing with the boat off (again, if I'm reading his initial post correctly).

 

[FSH 210 Sport]

Right on….

The only way to know for sure how much of a draw there is, is to install a shunt like this.

See post #78 here: https://jetboaters.net/threads/conversion-to-lifepo-batteries.35834/page-4#post-630936

Doing the math on sound systems is relatively difficult because their draw is not linear like an electric motor or a MFD. I have had great success with those Victron Energy shunts, they are simple to install and very easy to use. The app for your tablet, IPad, ,IPhone etc. is free and covers all of their devices.

I keep meaning to write up a definitive post on flooded lead acid battery maintenance / charging… they are simple batteries but do need just a bit of proper care to make them perform at their best.

 

[adrianp89]

Umm - dead batteries don't charge in 1 hour. Give it at least 24 hours on a charger.