Mixing AGM and Sealed Acid Batteries

full_mosey wrote:
The answer is NO, you don't want to mix FLA with AGM.

Here is what has not been mentioned so far.

AGMs rest at 13V and FLAs rest at 12.65. If you leave them connected in parallel, the AGM will sacrifice Amps to keep the FLAs at 12.65. After some time, the Volts of the AGM will balance out to 12.65. At that point the AGM will be around 65% charged.

What is the correct charge Voltage?

What is the correct float Voltage?

I got my first AGM in 2009 and within one year went 100% AGM.

HTH;
John

The house (agm) and chassis (fla) are not connected unless charging.

I still confidently say it is fine as proposed by the OP.

BTW this is a bit of a zombie thread. What did the OP do?

If the battery type/volts are mismatched, a bidirectional voltage sensing solenoid relay can keep the differing batteries separated during discharge/storage.

The relay is designed to sense that one of the banks is being charged by detecting 13V+ from either bank. Only then are the two banks joined in parallel so the charge can be shared.

That was clever of pnichols to search out compatible batteries.

HTH;
John

P.S.:

My coach's AGM deep cycle batteries rest - when fully charged - at 12.7-12.8 volts, which is right in the range where the engine starting battery terminal voltage rests when it's fully charged.

However, I selected my coach AGM batteries very carefully to make sure that I chose ones that would be compatible with a liquid acid starting battery and compatible with my RV's single stage converter for both their charging and floating.

Ideally, the ultimate is to use deep cycle AGM batteries in the coach and AGM starting batteries under the hood ... again assuming that both AGM battery types are specified to have close to the same at-rest fully charged terminal voltages.

The answer is NO, you don't want to mix FLA with AGM.

Here is what has not been mentioned so far.

AGMs rest at 13V and FLAs rest at 12.65. If you leave them connected in parallel, the AGM will sacrifice Amps to keep the FLAs at 12.65. After some time, the Volts of the AGM will balance out to 12.65. At that point the AGM will be around 65% charged.

What is the correct charge Voltage?

What is the correct float Voltage?

I got my first AGM in 2009 and within one year went 100% AGM.

HTH;
John

We've had mixed batteries in our Class C for over 10 years. The single engine starting battery is a regular Ford OEM liquid acid starting battery. The two coach batteries are AGM deep cycle batteries.

Whenever the motorhome's engine is running, all three batteries are direct connected together in parallel by a solenoid switch that is activated by the engine ignition key.

Winnebago designed our motorhome's system this way and it has worked just fine as far as treatment of the batteries is concerned. I have installed voltmeter and ammeter guages right on the cab's dash that show me how things are going with all three batteries at all times - whether parked or going down the road.

These meters read just fine at all times when on the road .... EXCEPT when the solenoid switch contacts become corroded after years of use. Just last year I had to install our 3rd solenoid switch because the voltmeters on the dash indicated that the engine battery was getting over 14 volts from the alternator, but the coach batteries were intermittently reading only around 12.8 volts when the engine was running.

I'll bet that this solenoid in many motorhomes is letting owners down and that they don't even realize it other than arriving at non-hookup campsites and noticing that their coach batteries don't seem to be fully charged - or hold a charge long after making camp - because they weren't getting charged well from the alternator. If this situation goes on too long the coach batteries will not have as long a life as they are capable of because they go too many hours under-charged on camping trips or are not fully charged when put into storage after arriving home from camping trips.

missnmountains wrote:
I agree, it does not answer my underlying question of whether or not I can mix AGM with Sealed Acid Batteries. I was responding to whether there was a switch on the charger. It appears to be automatic. As I indicated earlier, I will need to check with Jayco to determine if the house charger charges the chassis batteries. Unless someone on this forum knows the answer.

Thanks

Ken

Ken, if your MH has a BIRD (Bi-Directional Isolator Relay Delay) then yes, your charger is charging all batteries in your MH, including chassis. Check to make sure, if you have this, you need to keep all batteries the same.

missnmountains wrote:
I agree, it does not answer my underlying question of whether or not I can mix AGM with Sealed Acid Batteries. I was responding to whether there was a switch on the charger. It appears to be automatic. As I indicated earlier, I will need to check with Jayco to determine if the house charger charges the chassis batteries. Unless someone on this forum knows the answer.

Thanks

Ken

The simple answer is you want the house to be all the same batteries and you want true deep cycle batteries for that application (not marine).

For the starting batteries, you want regular starting batteries.

Go ahead and put AGMs in the house and and use flooded batteries for the chassis.

Another note on house batteries: Most flooded 12 volt batteries are not true deep cycle....they are a hybrid that works for starting and better than a starting battery for the house, but not well. In fact I have yet to see a true deep cycle flooded 12 volt battery. If you want to go true deep cycle, you need to go to 6 volt golf cart type batteries which are quite economical.

If you go AGM, the above statement does not apply. Lifeline makes real deep cycle 12 volt batteries. They make real deep cycle 12 volt batteries.

Ken,

Very few RV's converters charge the starter battery.

I added a trik-l-start to my class C.

The 9200 can have a 'wizard' added if you don't have one already.

The wizard allows you to set the unit to output 14.4, 13.6 or 13.2 volts.

Do you have a wizard?

14.4 is a good charge voltage for agm. 13.6 is a good float voltage for agm.

I chose to have all batteries the same when I was using flooded batteries. Since the starter batteries are maintained by the alternator and are isolated when the RV is not running you can mix flooded start batteries with agm house batteries.

It would not be best practise to have both flooded and agm in the house bank. It is possible with isolation switches--but I can see no reason to do so.

missnmountains wrote:
As I indicated earlier, I will need to check with Jayco to determine if the house charger charges the chassis batteries.

I thought you said you were going to check it with your voltmeter.

The 'house charger' requires AC - and for the manufacturer to assume you are always going to have AC when driving down the road seems a large stretch. Can it recharge them when on AC, that would require a way to defeat the battery isolation circuit and why would they add that cost and complexity for a battery that is designed to never be run down in the first place?