Battery #2 won't crank, voltmeter jumping

[SloBurn]

As stated, battery#2 won't crank engine and barely runs radio. When running and switched to just battery#2, dash voltmeter jumps constantly. I suspect a bad battery cable, but before I tear it all apart, I wanted some other opinions. Thanks!!

 

[1990-270-da-lover]

Have you run the boat with the bat. switch on both to make sure both batts. are charged? Coould be the #2 bat. is low and needs to be charged up, if you've been using just the #1 bat. Also check to make sure the alternater is charging the batteries, could be that if you have a lose cable as you suspect, the #2 bat may not be getting a complete charge. JMHO

 

[SloBurn]

Yes, I've run in "Both" position, and battery was good when first installed. Voltmeter reads 14V when running on batt #1. No problems when starting on #1. Voltmeter OK when running on "Both".

 

[JimG]

As you say could be a battery cable connection or simply a bad battery. Welcome to CSR!

 

[SloBurn]

Thanks Jim I Just found this forum today and thought I'd ask a ? before I have to stand on my head to get to the battery and switch. I think it's the cable itself, not the connectors, as they are clean and covered with Vasoline to protect them.

 

[wakeup 19]

measure voltage of battery 2 isolated when off then running. should be 12.5 or so when not charging and 14 plus when charging. If it is not at 14 then cable if battery 1 is reading 14 when charging.

 

[SloBurn]

OK, so I got out my ohmmeter and measured resistance on Batt#2 ground cable. ~ 2.5 ohms...too much!! Bought an $8 cable and hooked right up from Batt terminal to engine block in front....and charged Batt #2 for 20 minutes, and it now starts up boat!! Left overnight and tried again, starts right up. I got lucky I think, first cable I checked and replaced was the bad one, and also the easiest to get to.