adding batteries question 2008 260DA

[jrseitz]

I did a search on batteries and found some good stuff but now I am more confused than when I started searching. The PO of my 260DA installed a 2000w inverter on the boat with two large wet batteries. I just took the boat in for repairs at B&E marine, for the first time to B&E, in Michigan City (it seems like they are good honest folks) and they told me the inverter didn't have a spark arrest so they disconnected it. I am fine with that but I want to know if there is a way to use the one or both of the big batteries as an extra house battery? Is it possible to connect one or both of them to the two original batteries that came with the boat? My battery switch has a 1, 2, both and off selector. Can you simply use a short cable and connect two batteries on one bank? Can I put both original batteries on one bank and the two larger on the second bank? Or should I just find someone who needs one or two good batteries and get rid of them? I am technically challenged especially with electric stuff.

 

[BerettaRacer]

Let me start off by saying I'm not familiar with your particular boat or your system, so take info with a grain of salt, and do with the info as you see fit.

The general rule with batteries is that if you connect the batteries in parallel, (pos to pos & neg to neg) you increase capacity, similar to using another battery to jump start your car. If you connect in series, (pos to neg) you increase the voltage, similar to stacking batteries in your flashlight.
That being said, I wouldn't "just use a short cable and connect the batteries" without an electricians advice. Mis connected batteries can be dangerous, and cable size has to be matched to load to prevent fire hazard etc etc.
It can be done, and you could gain many amp hours to your battery draw down life, but get a professionals advice/assistance. YMMV

 

[testlab]

Is it possible to connect one or both of them to the two original batteries that came with the boat?

No. Do not connect batteries of different types together. You must only connect together batteries of the same type and similar age and condition.

Can I put both original batteries on one bank and the two larger on the second bank?

This is what I would do providing the original batteries are the same. To make two separate 12V banks, connect the pairs of batteries in parallel (+ to + and then -to -) and then connect the joined + to the 1 or 2 position on the switch.

 

[electricaldoctor]

Just to add to the advice offered above is that your bank will only be a strong as the weakest battery in the bank. In other words, do not install a fresh battery with an older one as it will get pulled down to the weaker battery's level. Build your bank with new batteries of the same type and specs.

 

[2000SEARAY280SS]

Sounds like you have additional batteries all ready.

My first question would be how are the old inverter batteries being charged?

Also if the previous owner installed a non-ignition protected inverter I would suspect everything about the previous install.

If you are not installing any additional loads that require the extra 12 volt capacity the additional batteries would provide I would pull the inverter batteries and gain the space and loose the weight.

If you want additional capacity then I would double up the factory installed house battery or try and get the highest aH deep cycle rated battery you can find.

 

[jrseitz]

Ok lets see if I have this correct. The additional batteries that were connected to the inverter were new 8/2011. They are much larger in size than the original batteries that were installed in 7/2010. The boat is a 2008 model sold new in 2010. So I could take the two original batteries and connect them together on bank 1 + to + and -to - and take the other two and connect them together on the 2nd bank the same way. I would have each bank with two batters of the same type and age on each bank. I have the space to do this with the batteries all sitting on the starboard side of the boat. It would create some weight issues??? I do have the 28 gallon water tank on the other side that would help balance out the weight a little. I would probably be ok until I have any one sitting on the starboard side, which is where all my seating is... Any thought to just replacing the original batteries with the two larger ones and sticking with a two battery system? The inverter batteries are dc31dt. That is the only number I could find other than a little note that said they could handle 23w for 225 hours. I am still confused on this one and don't want to toss a couple good batteries if there is a functional use???

 

[2000SEARAY280SS]

I do love these battery posts.

Here are some of the things you will need to consider when doing what you are thinking about doing.

By doubling the batteries you have increased the load the alternator needs to charge. The factory installed alternators are not designed to be a full time heavy amp draw charger. They are there to top up the starting battery and maintain it while the battery powers the engine electronics and sensors and its secondary function is charging the house battery.

If you do not add an Automatic Charging Relay ACR the alternator could be overloaded when replenishing the amps removed from the house batteries while the engine was off. The ACR manages the batteries connected to the alternator and allows the starting battery to be fully charged before adding the house bank. This essentially lowers the demand on the alternator and removes the need to play "what position do I need to put the battery switch in".

I would not double up the starting battery. If one cell in the bank goes bad it can damage the good battery leaving you with two batteries to replace. This happened to my inverter bank.

Starting batteries and deep cycle batteries serve different functions. I always like to use a dedicated starting only battery over a combination deep cycle/starting battery. I feel I get the type of high short amp draw I need to power the starter and I am not using the deep cycle portion anyway. I am not sure if your starting batteries are dual purpose or not.

If you are intent on maximizing the batteries you have I would go with a single starting battery and a double house bank with an ACR add a battery from Blue Sea. It works for me.

http://www.boemarine.com/blue-sea-7650-add-a-battery/ :grin:

 

[jrseitz]

Thanks Mike. Great information. I think that I will leave well enough alone and not try to mess with it. I have removed all of the inverter wiring and made enough room to store my Magna grill where the inverter batteries were. This site is a great place to bounce ideas and ask questions and I appreciate everyone who did that.