Need battery advice

My cranking battery would turnover engine after running the anchor light for about 30 minutes. It started the engine fine the three times prior to running the light, the engine was also ran for atleast 10 minutes after each start.

When I got home I put plugged in the onboard charger. After charging for about 12 hours, I unplugged the charger and checked the voltage. The trolling battery had around 13.4, while the cranking had about 12.6

I proceeded to do a few tests scenarios:
Turned on Running lights only (anchor light unplugged) battery voltage 12.4
12.3 volts at 11:34
12.24 volts at 12:39
Cutoff running lights at 12:40 voltage 12.45 at 12:45

Turn on anchor light only, voltage 12.32 at 12:46
12.27 volts at 1:06
11.23 volts at 3:36

Cut lights off , tried to crank. Turned over very slow but wouldn't start. Voltage at 10.4 after attempt.

I'm guessing I can run it to an autozone type store and have it checked? Thanks in advance for any advice.

Gone, time for a new one. I run stuff all day long, like 7 or 8 hours and then fire up a 200hp and head in. 2 depth finders, aerator constant and a cd player most of the time.

Rees what group size battery do run ?

Thanks guys. Guess it's time to sort through the brands. Lol

Quote:

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Originally Posted by Redge

Rees what group size battery do run ?

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I run group 31s cranking and 12V golf cart batts for the troller.

Batts are just as important if not more important as any tackle you have in your rig.:twocents

Rees I am running a group 27 for cranking, will a group 31 give me ?% more power for the day? ie any way to know how much longer a group 31 would last over a group 27, just looking for a SWAG. Thanks for your time.
Don't mean to hijack the thread, do think it is pertinent.

Quote:

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Originally Posted by Redge

Rees I am running a group 27 for cranking, will a group 31 give me ?% more power for the day? ie any way to know how much longer a group 31 would last over a group 27, just looking for a SWAG. Thanks for your time.
Don't mean to hijack the thread, do think it is pertinent.

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You can't know for sure without comparing RC ratings. Some 27s are as small as 160 minute RC and some 29/31 are as big as 225 minute RC. Typical 29/31 are 205 minutes RC. Battery weight is a good indicator of capacity. You can't ignore CCA though, because some newer outboards have significant cranking amp requirements.

Watch out for the Deka 31s. They rate their RC at 23A which inflates the numbers.

If the battery checks good do a voltage drop test on the battery cables. What happens some times is they get corroded inside the lugs where you can't see it and will cause problems identical to what you are having. Sometimes you can see just a little corrosion at the base of them which can indicate possible problems. The voltage drop test is the Cadillac of tests for wiring.

The above is true. Another quick check is to try cranking then grab the cable near the lugs with your hand. If it is warm/hot. Change or make sure no loose connection.

Here is the update. I let the battery charge all night, it was at 13.6 volts with the charger on. As soon as I unplugged the charger, the voltage dropped to 12.6 or so I turned all lights and electronics on. The voltage didn't drop a lot immediately and looked somewhat normal (to me) , but after about 2 hours it began dropping rapidly. I took it to O'reillys and they confirmed that it was bad. I did replace the battery with one from Advanced Auto Parts that has an RC rating 135 with the cranking amps at 800 and 1000. I know I didn't get a great battery but the one I pulled out was only rated at 75 RC with 400 and 500 on the cranking amps. Plus I had a promo code for there so I got the $89.99 battery for about $60.

Thanks to everyone for there input, it will definitely be helpful in the future.

Catfan thanks for the info.

Tigerfanatic, a carbon pile battery tester is a wise investment. You can buy one at harbor freight for around $50. I've had good luck with the group 31 marine batteries from wal mart.
500 Amp Carbon Pile Load Tester

Thanks justinp, never thought about buying one of those. I probably should have got a 31, but went back with a 24.