Hi Jean & Erwin,
I’m pretty sure that was a defective battery you suffered, rather than any defect in the “system”. I’ve run this system for eight or nine years, with two different sets of (albeit budget) leisure batteries with no problem whatsoever. I showed you the forum where many people were running twin (and even three!) batteries from Electroblock EBL99s, so I’m pretty sure it’s OK. Number 2 battery is fine, isn’t it, and I think that would have suffered too if it had been a ‘system’ problem. The B2B does nothing more than put a varying charge into the batteries quicker than a battery charger does, balancing that charge with any rise in temperature, that’s all. Martin doesn’t like them – he argues that just uprating cabling will achieve the same benefit at a fraction of the cost!
But… I think, as ‘newbies’, that you should act on advice from Martin – he knows far, far more than I will ever know!
As far as “batteries” are concerned, there are two that I would seriously consider, both highly recommended by Martin – the Varta LDF90/Bosch L90 (same battery)…
(https://www.tayna.co.uk/leisure-batteries/varta/lfd90/ )
and the newer Yuasa L36EFB…
(https://www.tayna.co.uk/leisure-batteries/yuasa/l36-efb/ )
I don’t think any AGM batteries are recommended by Martin – he points out that, despite being allegedly “sealed”, they still gas-off, whereas the Varta and Yuasa don’t – much safer in a motorhome! Lithium may be a step too far (expense wise) until you have more experience? I don’t know – your decision.
Good luck with sorting this, Jean & Erwin. As you really are new to all this, I would go with Martin’s advice. I know some people don’t always agree with him but in my opinion, his recommendations come from good, solid experience.
Barry