I hve in caravan a Bosch deep cycle gel battery being charged by solar panels when off grid . The solar controller powertech model 3739 said may only be used for charging and controlling lead acid batteries. This instruction was inside operating manual under heading "safety". It was not written on box unit came in so what is situation have i bought wrong?

A gel battery is still a lead acid type, except the acid solution is a gel instead of a liquid.

The maximum charge rate for a Bosch gel electrolyte lead acid battery in cyclic use (not standby unused) is 20 amps @ 14.4v to 15vdc @ 25*C. The voltage must be reduced by 0.3v per degree over 25*C at the battery, not the outside temperature. The battery will always be hotter when recharging and discharging than the ambient temperature due to the chemical reaction occurring inside.
40*C battery temp means 40 - 25 = 15 x 0.3 = 4.5v. 15v - 4.5v = 11.5v .... so you basically can't recharge them when it's hot. I have 2 dead ones in the workshop that the installer didn't understand what was written on top of the battery for all to read.
Gel batteries do not suit RV use in Australia, it's just too hot here. Even in stand by use they need to be in a temperature controlled room.
If the battery is new, you just bought it, take it back and get either an AGM battery or a flooded cell battery, just be careful about where you mount it because of the acid fumes and hydrogen/oxygen mix that comes off when charging or discharging them.

T1 Terry

T1 Terry. You say Gel Batteries do not suit RV's, BUT, Jayco use a 100A/H GEL battery in al their new caravans & campers (thousands of units per year).

Yes Jayco use or used gel batteries in their vans, I had to replace both batteries in our van a Jayco, cause we had very little charged capacity from them. I put 2x AGM's in their place and are much better off. My understanding was that if a gel battery had to be charged very slowly, using a fast charge created gas bubbles in the electrolyte, and being a gel the bubbles remained around the plates, this ruined the battery. An AGM battery is more tolerant in the charging process.

That is correct as far as I understand it too iana, but remember Jayco only put one panel at best on a van and use that all in one electrics/charger thing to recharge them from 240vac when at a caravan park. Those things put in 10 amps @ 13.8v on a good day, more often than not it's more like 5 amps to a max of 12.8v. If the owner increases that solar or mains charging then it's not Jayco's fault the batteries were not suitable for that. Gel batteries can not handle a high rate discharge either because that causes hydrogen and oxygen bubble to form between the gel and plate material. Anything greater than a C20 discharge rate (5 amps from a 100Ah battery) is running the risk of forming these gas bubbles. Once the gas bubble is formed it is virtually there for life, with no contact in the spot where the bubble is means that part of the plate has no connection to the electrolyte and forms a sulphate layer at that spot. Every bubble reduces the surface area contact between the plate and the electrolyte resulting in a loss of capacity and ability to discharge or recharge by that amount. Bugger all to start with, but as more bubbles form the greater the action across the remaining electrolyte to plate area resulting in more bubbles forming, the death spiral.

T1 Terry

What a crazy set of charts, all published in a manner that looks similar to other charts but if you read what the actual X and Y axis represents. The "Endurance in cycles" graph is one of these, it looks like a cycle life chart but a closer examination it actually shows the max number of cycles you can get with a sliding scale of the capacity the battery will have at the 100% state of charge point if the IEC-896-2 test procedures are used ... but no reference to just what those test procedures are, so it really doesn't give much information at all.
The "temperature effects on capacity" what does 0.05C actually mean? They specify a CA rate for charging in the current column in the charging graph, so they clearly know the difference between C and CA, so C is used in the same graph to symbolise temperature in Centigrade, so it can't also mean *C, so does it actually mean anything other than technobabble?
The Charging chart is the most interesting, if you actually look closely at what it's telling you, basically within 4 hrs charging from completely discharged @ 13.8v the current has dropped to 0.12 CA (12 amps for a 100Ah battery) and falling yet the battery is only at 60% SOC. To get back to 100% SOC will take 18 to 20 hrs. At the end of 6 hrs the battery is only at 80% SOC and dribbling in less than 5 amps, so forget about solar recharging, the sun just doesn't shine long enough, even if you can keep the battery at 25*C or less.
As for the bit about recombining hydrogen and oxygen to prevent dry out, WTF???? if it is Gel battery then how do the oxygen and hydrogen bubbles get to the recombiners, and even if they somehow could, the recombined gasses create pure water, how does that mix with a gel electrolyte? The gel doesn't become a liquid when it's convenient yet stay as a gel when that is more convenient, it is one or the other, it can't be both

T1 Terry