Replacing batteries advince needed

[mr300z87]

So I am looking to replace 1 of my 2 batteries this season and the other in the spring next year so that so I have a 1 year stagger between them. These are for a Sea Ray Sundancer 250 with a Merc 7.4L (see project thread in signature file). The batteries in her now are the ones from my other boat that is now in dry dock with engine issues. I have group 24 marine Start battery date 2013 and I think a group 27 deep cycle dated 2011. Both batteries seem to hold charge, and I do have an on board charger. The question I have is do I replace the newer start battery now with a Group 27 and then stick with deep cycle until next year? or Do I replace the Deep Cycle now the Start battery later? We do go out and anchor for a few hours at a time with the radio playing. I am sure some will say just replace both or wait until one fails. I just don't want to have a dead battery after an awesome day on the water and have to call sea tow. As always any advice in greatly appreciated. Mike

 

[alldodge]

I just don't want to have a dead battery after an awesome day on the water and have to call sea tow

You have several questions inside your questions. Your radio and accessories should be on your house (deep cycle) bat, so if it starts to fail this should be of no concern in cranking the motor up. The start battery should not be connected to the deep cycle. I would not be concerned with the radio dying, but would be if it did not crank up. My main concern would be the crank battery.

If you check your bats it will give you a heads up when they start to go, and they both won't go at once. Now if you have a battery switch to connect the two together, this can usually get you going if there is an issue. Check the bats once or twice a month after the charger is turned off for a couple hours. Could just check the charge of the start battery after playing in the water and getting ready to head back. If the voltage is below 12.4V after sitting unused for several hours, start looking for new batteries.

You have had several years for the crank, so I would have already replaced it being a lead acid if it was in my boat. Mine eats batteries, but looks like yours does not. Use to get 3 years maybe from lead acid, I changed to AGM's and now I'm on year 6 and still check good

 

[KD4UPL]

I've gotten over 5 years out of batteries and I don't charge them over the winter. I would bet a G27 deep cycle has enough MCA to start your engine. I always ran 2 identical batteries. I'd use batt 1 one day and Batt 2 the next. I charged both underway. If I killed one I could start the boat with the other. Since the bstts always charged in parallel I wanted them matched in size, age, type, etc.

 

[mr300z87]

AD thanks for the reply. The boat is equipped with a 1, 2 or both type swtich just like my old boat. Ussally I start and run to my destination on both to charge both (old boat had no onboard charger) then swtich to the deep cycle while anchored then back to both for the start and ride home. I think I will replace the start battery this year just to be safe and the deep cycle next srping before launch. But before I do anything next time at the boat Ill turn off the charger and run a radio load on the battery for a while and check the drain on both of them. I would assume that a group 27 or 29 deep cycle would start the big 7.4L if needed.

BTW AD how is the Formula running??

No boating today my daughter is having a BBQ at her home in the Poconos so it will be a long day of driving.

 

[dingbat]

Install an "add a battery" kit and don't look back.

Automated charging. No more monkeying with battery switchs. Turn it on in the morning, turn if off when done.

Running two grp. 27 deep cycles. Full compliment of electronics. Sonar x 2, chart plotter, radar, etc. 8-10 hours on the troll no problem.

 

[alldodge]

BTW AD how is the Formula running??

She running good, thanks for asking, but every time I look into something I find something not right. Latest is I installed a oil temp sender and larger oil cooler. The new cooler is keeping the oil below 275 degrees or so. So need to install an even larger cooler to get it down in the 220 area. Temps being measured before the cooler. So what I found out is the cooler installed by the builder which was smaller then the one now was roasting the oil and I didn't even know.

I second the add a battery (ACR) suggestion. Installed one this season to replace my isolator, works great. Should have listened to Bruce a few years ago