20 Amp dc/dc charger

Your user guide will tell you what your existing charger will do. Most 20a dc chargers like the ctec 250 will administer to up to 300ah of battery bank. 210 ah should be bread and butter for most of them.

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Hi Marty,

It would be quite OK to connect a parallel battery of the same type but bear in mind that your charger will only deliver a maximum of 20A to be shared by the batteries.
You will have doubled your storage capacity but not your charging.

I had a Redarc 1220 DC-DC charger in my last rig (Landcruiser) and used it to charger 2 AGM batteries of different brand, age and capacity. One was a 120a/h Fullriver I bought around 2002/3 and the other was a 100a/h Redback that I bought in 2010.

The Redarc handled the charging duties quite okay and I never had ANY issues whatsoever.

The batteries had the job of running my 40 litre Engel 24/7/365 as well as occasional air compressor work etc.

Roachie

HI
Just make sure u have at least b&s cable feeding the charger .
No need to buy a different unit till the current one dies . At that point it maybe worth considering a larger charger 30-40 amp .

swamp

Thank's for replies , Roachie I may be in the same boat as you were ! . Instead of scoring a Fullriver 105dc , my mate has given me a 120ah Fullriver dc , all the same except amperage . I tried it out a bit with my shed based 20amp and 2.7 amp standard chargers and couldn't detect any voltage or temperature issues , smart charger might not like it though ? , cheers.

Most batteries like a charge 'rate' of 10% [or a little less] of their capacity so a 20amp charger is right on the money for the capacity you have envisioned , any bigger as in a 30/40 amp charger will of course charge the batts a bit quicker BUT at the detriment of battery longevity…...

Thank's Swampy , yes ive used 6 gauge B@S wiring throughout , ive also used a manual reset on/off type circuit braker .

HI

charge rate of AGM
20-30% of capacity 20-30 amps per 100ah of battery

charge rate of flooded [wet cell]
10- 20 % of capacity 10-20 amps per 100ah of battery

The charge rates are typically higher for AGM than wet flooded .
This is an advantage for Agm style of batteries ,why not take advantage of it .
In saying that apparently Agms have a small amount of fluid so not ""amping up"" to the max would be a precaution and with correct voltages to prevent fluid boil off . The lower regions of say 20-25 % would be good idea .

Always refer to battery makers instructions .
Not all chargers are ideal for all batteries all the time .

A lower amp charger will just take a lot longer
EG at 15 amps charge rate ,a lot of time will be needed to recharge say 100ah at that rate via a dc to dc 8-9 hours . Or at 25 amps 5-6 hrs

swamp

Normally id be using about 50Ah a day , on a bigger outback trip id be probably double that ( Extra fridge ). Quite often I drive 500-1000 km a day so I could switch the charger from one battery to another halfway , I thought doing it together would just save me mucking about ! , cheers.