Battery not getting sufficiently charged

[dominator]

I have 2001 SAN with two batteries and a perko switch. I have an amplifier and four tower speakers connected directly to the second battery. The boat also has an original 55 amp alternator. I already had to replace second battery after just 2 seasons, and now new battery that I got last year showing only 12.25v (vs 12.65 on the other battery that is 5 y/o). I tried alternating batteries on a perko switch and this year was running exclusively on ALL
mode, but it seems as if that doesn’t matter - second battery is not getting charged sufficiently or getting somehow discharged.

Trying to figure out if it’s a wiring issue and I should wire amplifier and tower speakers to the perko switch, or is it my alternator not being powerful enough and I should upgrade to 100A alternator? I am planning to addd a boom box and connect it to an existing amplifier and I’m afraid it will exacerbate the problem.

[jpwhit]

It's not likely the amperage rating of your alternator. 55A is more than enough. The alternator could be failing, but if that were the case you'd more than likely be having issues with both batteries. What is the voltage reading on each battery when the engine is running between 1500 and 2000 rpm?

[bturner]

Running the battery in both is typically a bad idea and is there as a means of connecting both batteries in case you have a low starting battery and need the extra amperage to start and get home. At best with "both" selected you're splitting the charge output between both batteries. At worst a bad or degraded battery will pull down a good battery. The better option would be to remove the selector switch and install an automatic charging relay. They're fairly cheap and easy to install. I've been using these for the last 15 years and haven't had an issue with any of the installations.

https://www.amazon.com/dp/B000RZNP5K...1d8f9bb6f&th=1

Will this resolve all your problems? If the charging circuit is good and you're not doing anything crazy like running your 1000 watt stereo for 6 hours straight at the sandbar then driving straight home and putting it on the lift for the day, then probably. If you're severely depleting the battery then not giving the battery time to charge nothing is going to fix that type of use case other than an external charger and even then severe use and the charging cycle will eventually wear the battery out.

Past the charging circuit, you may want to look at the type of batteries you're using. At the risk of starting another "what's the best battery thread" there may be a better battery solution for at least the stereo battery than what you currently have installed.

[dominator]

It's not likely the amperage rating of your alternator. 55A is more than enough. The alternator could be failing, but if that were the case you'd more than likely be having issues with both batteries. What is the voltage reading on each battery when the engine is running between 1500 and 2000 rpm?

I think voltage on the good battery was around 13.8v in ALL position, and around 14.5v in 1 position (good battery). I ran this test last time I was on the lake, and the boat is in storage now. I am not sure what running voltage is on bad battery when isolated (position 2)

[dominator]

Running the battery in both is typically a bad idea and is there as a means of connecting both batteries in case you have a low starting battery and need the extra amperage to start and get home. At best with "both" selected you're splitting the charge output between both batteries. At worst a bad or degraded battery will pull down a good battery. The better option would be to remove the selector switch and install an automatic charging relay. They're fairly cheap and easy to install. I've been using these for the last 15 years and haven't had an issue with any of the installations.

https://www.amazon.com/dp/B000RZNP5K...1d8f9bb6f&th=1

Will this resolve all your problems? If the charging circuit is good and you're not doing anything crazy like running your 1000 watt stereo for 6 hours straight at the sandbar then driving straight home and putting it on the lift for the day, then probably. If you're severely depleting the battery then not giving the battery time to charge nothing is going to fix that type of use case other than an external charger and even then severe use and the charging cycle will eventually wear the battery out.

Past the charging circuit, you may want to look at the type of batteries you're using. At the risk of starting another "what's the best battery thread" there may be a better battery solution for at least the stereo battery than what you currently have installed.

I do know that it's probably not good to run on ALL position, but I started doing this after new battery died. I also got tired of switching from 1 to 2, and I think you are right about bad battery pulling down a good battery.

Really like an idea of installing Blue Sea kit. If I go that route, I still need to connect my amplifier to the Blue Sea kit vs directly to the battery, is that correct?

[MLA]

https://www.harborfreight.com/9-func...ity-59410.html

This will tell you what you want to know, which we cant. Is it a charging issue? Bad switch? Failing cable termination? The meter will identify all of these.

With that said. Once the issue is identified and resolved, I would relocate the amp's B+ from the battery to the common output of the switch. This does two things. A) when the switch is off, there is no voltage to the amp. This eliminates any potential parasitic draw. When using the boat, you can decide which battery everything draws from.

No issue being in the ALL position with engine running.

I would pause on any modifications, additions or changes until the root issue is fixed.

[jpwhit]

I think voltage on the good battery was around 13.8v in ALL position, and around 14.5v in 1 position (good battery). I ran this test last time I was on the lake, and the boat is in storage now. I am not sure what running voltage is on bad battery when isolated (position 2)

Unfortunately, to figure out the issue, the running voltage on the bad battery with the switch in position 2 is the most important data point.

If your boat doesn't have an automatic charge relay, then you need to be in the All position when the boat is running. If you don't, then both batteries won't be charged. There is nothing wrong with running in the ALL position when the engine is running. It's just not a good idea to leave it in the ALL position for long periods of time when the engine isn't running.

If your "bad" battery has been completely drained a few times, then there's a good chance it's damaged. Especially if it sat completely drained for more than a few days. If you completely drain a lead acid battery 2 or 3 times, it'll typically be damaged. Doesn't matter how old it is.