Alternate location for additional batteries, Tab 400 Boondock

johnny_swindle

Wan to to add additional batteries other than on the tongue. Has anyone done this?

N7SHG_Ham

Pretty limited space, you could about double capacity by swapping the AGM for same amount of LiFePo4, going to run about $2k, but might be easier than wiring in additional AGM.

Awca12a

Before I’d add batteries to the tongue of a 400BDL, I’d get a goal zero and store it in the rear of the TV and use it to recharge the 400 as required.  

rfuss928

Some models of the DM T@Bs had their batteries located under the side bench or the bottom of the closet in vented boxes.

I fit a pair of AGMs in the closet location in our CS.

Just sharing an example of alternative battery locations.

Have fun!

Bob

ChrisFix

I'd think adding an extra battery under the bed where they already live is completely doable - just a trade off of how to use that space. 
The Wardrobe closet floor seems like a good location as well, weight distribution wise. You'd need to remove them to get to the service panel underneath, but that's doable as well.

What is the safe regular discharge % for the T@B 400 6V AGMs that come from the factory now? They are rated 235AH I believe, so what is the safe usable AH from them?
As soon as Lithium comes down in price a bit, I'd be all over those. 

N7SHG_Ham

@ChrisFix about 50% usable on lead acid including AGM so around 110-120ah. You could put a couple LiFePo4 in same space and have around 160-180ah depending on depth of discharge you are comfortable doing. You would shave about 2/3 of the battery weight off too. Of course that is going to take some coin to do, but if they last 10 years like they say, probably money ahead in 2029.

ChrisFix

N7SHG_Ham said:

@ChrisFix about 50% usable on lead acid including AGM so around 110-120ah. You could put a couple LiFePo4 in same space and have around 160-180ah depending on depth of discharge you are comfortable doing. You would shave about 2/3 of the battery weight off too. Of course that is going to take some coin to do, but if they last 10 years like they say, probably money ahead in 2029.

@N7SHG_Ham Thanks.
Is 50% discharge limit for AGM a soft or hard limit in your estimation? I ask, because I've ready a number of RV forum discussions on battery usage, and I thought AGM were stated to have a higher safe discharge % than conventional wet batteries?

Either way, LiFePo4 is definitely the near(ish)-term future for RV battery systems. I could imagine putting 4 100ah LiFePo4's under the bed and having a great dry-camping system. Could even run Air Conditioning for short periods with the correct inverter. Would probably have to use a generator to recharge for real dry camping, but if the generator is only for charging batteries, it could be pretty small (and light and reasonably quiet).
Just a matter of when prices come down not unlike what happened with solar panels, I think.

N7SHG_Ham

@ChrisFix everything I have read indicates that 50% for AGM too, I could be wrong, but I think that is about it. The lithium requires less time to charge too, so maybe the generator would have to run less time too.

Sharon_is_SAM

AGMs can recover more fully (relative to a standard wet cell battery) from a discharge over 50%, but repeated discharges over 50% will shorten the life of the battery, hence the recommendation of the 50% limit.

ChrisFix

A lot of sites say AGM has an 80% safe discharge rate (with the same duty cycle as flooded at 50% discharge). But I don't have any personal experience with how that plays out in the real world over the life of a battery. 
Splits the difference between flooded and LiFePo4...
Here is just one site (there are quite a few that say the same):
https://batteryuniversity.com/learn/article/absorbent_glass_mat_agm
"The leading advantages of AGM are a charge that is up to five times faster than the flooded version, and the ability to deep cycle. AGM offers a depth-of-discharge of 80 percent; the flooded, on the other hand, is specified at 50 percent DoD to attain the same cycle life. The negatives are slightly lower specific energy and higher manufacturing costs than the flooded, but cheaper than the gel battery."

DougH

I have Vmax AGMs in my 320S, and they provide the following manufacturer's data:

https://www.vmaxtanks.com/assets/images/technical info folder/Cycles VS Depth of Discharge.pdf

Switching from 50% to 80% discharge drops the number of cycles from 900 to 550.  Can probably be done occasionally, but one halves the battery life if done consistently.  At least for that particular family of AGMs.

rfuss928

Some real world experience:

We have been traveling in our T@B beginning in 2011 an average of about 60 nights a year.

If we depleted our batteries to 80% discharge every night we have spent in SUNT@B we would still have 3 or 4 more years life / cycles remaining based on those estimates.   Reality is we have rarely seen the SOC below 50%  but have spent days in the 70-90% range.

Our pair of Optima D31M AGM batteries have 2011 and 2012 dates.  I had them checked at the Interstate distributor last year and they both exceeded all original capacity specifications.

We don't "boondock" often but camp any where available whether there are hookups or not.  There are many more choices in many places, NPs especially, if you don't require hookups.  The roof mounted solar and these batteries have not let us down yet. 

YMMV

Have fun........

johnny_swindle

Want to thank everyone for their input. I believe I will follow @ChrisFix suggestion about putting the battery under the bed.  Once I get this done, I will post some pictures.