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Old 28-05-2019, 12:20   #1
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Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

My 2, 5-year old lead acid batteries will have to be replaced soon.
Meanwhile, I would like to add to 2 AGM batteries for the house, and use
the old lead acid for starting.
I will also be adding a max of 200 w solar and a 1500 w inverter.
I have a Atomic 4 engine.

1. Is using the older batteries a good idea for use as cranking/starting?

2. What type and size battery charger? I've been checking feasibility of charging 2 banks of batteries (2 batteries in each bank), but having trouble finding what I need--many chargers charge 2 banks, but a max of only 1 battery per bank.

3. Would using 2 chargers make more sense?

Thank you in advance for your input.
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Old 28-05-2019, 12:40   #2
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

Do you have a battery charger now? If so, which one?

Some of the newer ones offer several different charging profiles, and in some cases you can use a setting for one battery type that will also work well enough for the other type.

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Old 28-05-2019, 12:44   #3
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Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

You can do as you suggest, an issue is I believe that you will have to charge the flooded battery at AGM voltages.
I believe the old battery can start the Atomic pretty easily, and if it canít you should have a 1,2, both switch that let you change to the other bank and crank it then.

However Iíd suggest that maybe you really donít want AGM batteries, possibly GC2 golf cart batteries may be best for you, more durable, much cheaper and then your other battery will be charged at the correct voltage too.

Chargers that have multiple outputs are for charging multiple banks, and you can have many batteries in a single bank. They charge banks, not individual batteries, but could charge just one battery too if that is all there is in the bank, assuming itís the correct voltage of course.
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Old 28-05-2019, 13:00   #4
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

The only point of a dedicated Starter batt is utmost reliability, and nothing special nor expensive is required, so IMO no on that bit.

Going to a bigger new House bank would make more sense, with a smaller Reserve for redundancy, and cranking off either easy to rig.

AGM is lead acid BTW, but FLA is cheaper, more robust and longer lasting.

Multi-bank chargers are not required, just output to House, then a VSR or Echo Charger over to banks otherwise kept separate.

Making all batts matching is best, don't add new to old, charge voltage should be good for all concerned.
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Old 28-05-2019, 13:02   #5
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

It's an older Guest, 15 amp. Model 2815M
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Old 29-05-2019, 04:39   #6
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

Quote:
Originally Posted by Sailon1 View Post
It's an older Guest, 15 amp. Model 2815M

Do you have the manual? Does it offer you different charging profiles? If so, what voltages for each?

In general, it's best to know the exact voltages the charger will output AND the exact voltages your batteries (brand/model) want... so that means checking info from two different manufacturers. And batteries vary; for example, one brand of AGM wants X and Y for bulk/absorption and float voltages, while a different brand of AGM may want A and B...

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Old 29-05-2019, 08:25   #7
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

I don't even have my start battery connected to my charging system other than my Alternator. Since I only use it to start engine it probably puts back what I take out for a usual start up in minutes. This has worked well for three years and if I really need to I can jump from house bank


This lets you set your charger for your new bank. I do use my engine several time a week though.
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Old 29-05-2019, 08:31   #8
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

NO & NO!! Not a good idea to use old, presumably house, batteries as start batteries they have very different internal configurations. Start batt's are designed to give very high currents for short periods, house batt's should be deep cycle and designed to supply low to mod currents over long periods. It is all to do with the surface area and design of the plates. Also no you cannot simultaneously charge AGM or any sealed batt correctly on the same program as an open FLA they need different voltages. If you charge an open cell on an FLA cycle it will undercharge and die of sulfation. If you charge an AGM on an FLA cycle it will gas and loose water which will quickly kill it. Unless you are prepared to sequentially charge each bank and reprogram you charger evey time you are going to need separate chargers. You are also going to have a potential problem when the engine is running. You will need to set the alternator regulator for AGM. This will not correctly recharge the start battery however provided it is a dedicated start battery this should not be a problem as it should always be at least 80% DDC and should not be being cycled (which quickly kills start batt. Generally when running FLA's you have the reverse problem, the setting needed to recharge the deep cycle house bank are a bit high for the start batt so it uses more water. Not a significant problem as long as you don't fitt a sealed start batt.
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Old 29-05-2019, 10:10   #9
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

[QUOTE=roland stockham;2898306]NO & NO!! Not a good idea to use old, presumably house, batteries as start batteries they have very different internal configurations. Start batt's are designed to give very high currents for short periods, house batt's should be deep cycle and designed to supply low to mod currents over long periods.



Presumably being the key word. This is a older 30 foot. I have seen more of these with regular auto group batteries used as house bank than the other way. He should let us know what he has.
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Old 29-05-2019, 11:28   #10
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

[QUOTE=Valmika;2898384]
Quote:
Originally Posted by roland stockham View Post
NO & NO!! Not a good idea to use old, presumably house, batteries as start batteries they have very different internal configurations. Start batt's are designed to give very high currents for short periods, house batt's should be deep cycle and designed to supply low to mod currents over long periods.



Presumably being the key word. This is a older 30 foot. I have seen more of these with regular auto group batteries used as house bank than the other way. He should let us know what he has.

If that is the case and the existing batteries are auto/trailer type start or 'dual purpose' that have been used for a house bank then they are almost certainly dead or close to it. Would not be reliable as start batteries. Star batteries should not cost more than $100-150 so why not replace them with new
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Old 30-05-2019, 09:02   #11
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

Yes you can use your two old batteries in parallel as a single bank starting battery if you like, the Atomic doesn't take much current to start. But it may be better to buy a new starting batt in the long run. They are not that expensive.

Many boats are using two AGM batteries as house with the selector switch to connect either or both, as desired, to the DC house bus. The starting batt + is separately connected only to the ignition circuit and start motor. For charging, all charging sources, alternator, solar, AC charger, are tied into the common terminal of a MOSFET battery isolator or echo chargers.

We set our shore power charger to AGM parameters to match our house batteries and it does a fine job charging traditional lead acid starting and windlass batteries.
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Old 30-05-2019, 09:33   #12
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Re: Options for charging 2 battery banks: 2 old Lead Acid and 2 new AGM

The charge voltages for AGM and wet cells are very close. Not an issue. Want to see? Go to Balmar | Marine Charging Systems | Battery Monitors | Multi-Stage Voltage Regulators | High Power Alternators | Serpentine Pulley Conversions and download any regulator manual, like the MC-614. There is a chart with preprogrammed charging voltages. They are almost identical.



A 2 battery bank to start any small recreational vessel engine is overkill. Why lug around excess useless weight?


AGMs have begun to make less sense for some (not everyone). Why? They require more care, must be recharged fully and regularly and cost a LOT more for little discernible advantage (other than faster charging in bulk).


Here are some discussions:


AGM Batteries - Making The Choice (from Maine Sail)

https://forums.sailboatowners.com/in...choice.124973/

AGM Battery Issues and the Blue Seas Dual Circuit Switch (from Maine Sail) "DARN AGM Batteries"
https://forums.sailboatowners.com/in...teries.133773/

Additional Observations on the Limits of AGMs Electrical Systems 101
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