Yes, you can add another AGM, but how successful that will be depends on how old the existing one is.
Adding another battery is a bit like opening another bank account. You won't have any more money to spend unless you increase your income.
You may be much better off (and spend less money) by adding extra solar.
Cheers,
Peter

-- Edited by Peter_n_Margaret on Monday 19th of August 2019 03:05:08 PM

hPeter_n_Margaret wrote:

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Adding another battery is a bit like opening another bank account. You won't have any more money to spend unless you increase your income.

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 Peter,that is the best analogy I have seen in a long time.As always,you are absolutely correct,and Swamp got it right too....you should have an absolute minimum 150 watts Solar for every 100ah of battery storage.I have well over 300 watts Solar/100ah battery,and after running my AC or heater all night,my batteries are back to 100% by 7am in summer and 9am in winter.You never can have too much Solar.Cheers

I would have thought 280 watts of solar for a 100 amp battery would have be ample and a extra battery or two new batteries depending on
condition /age of original battery would be ok. mine works

not much point in producing a lot of power that you don't use with nowhere to store it. somewhere in the mix there is a happy medium

the op didn't mention what his power consumption needs are and why he thought he needed more storage

I doubt they are fully recharged by 7 am or 9am or even 1pm. More likely reached the end of the boost charging cycle at around 70% SOC and from there they continue to take in charge at a much slower rate. Even when the charge rate has dropped to around 5% of the advertised capacity (5 amps per 100Ah) it still takes a min of 24hrs holding the same float voltage to get from 98% to 100% charged. The only way to speed that up is pulse charging, and way too complex for RV use.

T1 Terry

T1 Terry wrote:

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I doubt they are fully recharged by 7 am or 9am or even 1pm. More likely reached the end of the boost charging cycle at around 70% SOC and from there they continue to take in charge at a much slower rate. Even when the charge rate has dropped to around 5% of the advertised capacity (5 amps per 100Ah) it still takes a min of 24hrs holding the same float voltage to get from 98% to 100% charged. The only way to speed that up is pulse charging, and way too complex for RV use.

T1 Terry

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 Hi Terry...All I can relay is that the meter that shows the battery charge level reads 100% full after dropping to around 94% overnight.Only once have I run the batteries waaaay down.As an experiment,when the temperature was forecast to drop to 5 degrees,I left the heater on all night at 30 degrees,and in the morning there was not much left in the batteries at all! They did,however,recover to 100% full (according to the meter) during the day. I have no idea what my solar man did,but there are gauges and switches all over the place and everything works brilliantly.I have no gas at all in the van,but run reverse cycle 2.5kw Mitsubishi Heavy Industries AC,microwave,electric jug,electric frypan,slow cooker,TV,175 litre fridge/freezer,air fryer etc with no problem at all.As I do not really understand electrics,all I can do is report what I see on my gauges,but any  comment on my situation would be appreciated? Always happy to learn from those who know what they are talking about. Cheers

T1 Terry wrote:

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What brand/model gauge do you use to indicate the state of charge in the battery yobarr? Sadly, many are simple voltage driven meters, so as soon as they see 13.8v they indicate a 100% SOC and this leads the operator into believing their battery is full again. Some meters use an even lower voltage, I've seen 12.6v quoted as being the battery 100% fully charged point, but that was by someone selling a product that was questionable regarding how well it really worked.
T1 Terry

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 Hi Terry...not sure of brand etc,and not presently at the van,but it regularly gets to 14.4 volts.Read somewhere that Lithium should not be left at 14.4 volts for too long(?) so I turn on the AC or heater for a few hours. Voltage then seems to drop to 13.2,or there abouts? Any advice is appreciated.Cheers.

-- Edited by yobarr on Tuesday 20th of August 2019 08:58:40 AM

Thanks everyone for the advice and information, it was very enlightening and helped me to work out something that I was not up with.
Regards
Bob

A little depends on how battery system is wired up ? If its connected to motor battery or charging system ? I suggest via a VSR ( voltage sensitive relay) and you drive a couple of hours a day it will assist in keeping charge . I fitted extra solar and havnt looked back !! Just paralleled extra panels to existing.,

T1 Terry wrote:

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yobarr wrote:

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T1 Terry wrote:

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What brand/model gauge do you use to indicate the state of charge in the battery yobarr? Sadly, many are simple voltage driven meters, so as soon as they see 13.8v they indicate a 100% SOC and this leads the operator into believing their battery is full again. Some meters use an even lower voltage, I've seen 12.6v quoted as being the battery 100% fully charged point, but that was by someone selling a product that was questionable regarding how well it really worked.
T1 Terry

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 Hi Terry...not sure of brand etc,and not presently at the van,but it regularly gets to 14.4 volts.Read somewhere that Lithium should not be left at 14.4 volts for too long(?) so I turn on the AC or heater for a few hours. Voltage then seems to drop to 13.2,or there abouts? Any advice is appreciated.Cheers.-- E

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Ah, if you have lithium batteries that is a whole different ball game, they will recharge to near 100% (97% to 99%)very quickly, the more solar the faster that happens

. It definitely sounds like you have a voltage driven state of charge meter, because the voltage only ever drops into the 13.2vdc range until seriously drained the 13.2v is interpreted by the meter as 92% SOC. You need a Victron BMV properly calibrated for use with lithium batteries so it actually counts the energy out against the energy in at the battery, and a solar regulator programmed to suit lithium batteries as well.

You are correct about not holding lithium batteries at anything more than about 14v (depends where it's measured but 14v at the battery terminals) and a method of stopping the charge if any cell hits 3.6v. 14.4v is 4 x 3.6v, there is very little chance that all 4 cell reach 3.6v at the same time and even less chance they will all stay at 3.6v if the charging holds them at 14.4v, one cell will always, and I mean always, run away resulting in the voltage dropping in at least one other cell to allow the high cell to continue climbing in voltage while still maintaining the 14.4v total. The fact the voltage drops rapidly to 13.2v is also not a good sign, something not right in the system, but virtually impossible to trace via the forum.

I think I've probably dragged this topic off track, that was not my intention, sorry about that.                               T1 Terry  

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 Hi Terry....Thanks for your information above.On my van I have 9x190 watt mono panels (1710 watts) Solar into 6x90ah Victron Lithium batteries (540ah). The inverter is 5kw Victron. The car has 1x190 mono into 1x90ah  Victron Lithium battery,and it has a 2kw inverter......I would like more battery in the car,but I have run out of room for more Solar and I am getting close to my 2300kg rear axle capacity anyway! (The 190 watt panels are about 18kg each?) My battery monitor is a Victron Blue Power BMV 702 and this morning it was showing 14.47 volts so I turned on the AC at 18 degrees.There is a flash Victron Blue Power control board that shows that the AC load is 240 watts,so there still is more power being produced than is being used at the moment! (Much more!) Does that all sound OK! Cheers.                                                                                .P.S Always your posts are informative,so I do not think that anybody would consider that you have gone off track! Any conversation naturally leads into another,and I am sure that I am not the only one happy to learn?