This article was first published on 14/1/2014. The second in a series of articles about my experiences with the electrical system and the leisure battery in my Motorhome.
I’m updating this as I dig out more data. To tell the truth I’m getting a bit fed up with the lack of datasheets and the standard of the data sheets that the manufacturers put out. My theory is the rise in the popularity of solar panels means that users can actually make do with any old battery and the suppliers will sell “any old battery” as a leisure battery at inflated prices.
In part one I explained how when we are engaged in general touring we do not need to use Electrical Hook Ups (EHUs) to keep our 70AH leisure battery charged up with no reduction in out normal power usage.
However this is not the only way the motorhome will be used. Sometimes we go to folk festivals. Now if the festival is only a weekend three days then its not a problem – as calculated we use about 7AH per day. We are unlikely to need to charge phones, tablets and laptops over the weekend so the battery should manage the 21AH quite happily (provided its in good condition).
BUT some festivals are longer – a week or even a fortnight. How are we gonna manage?
Data collecting again
The PDU and the fridge igniter between them are taking 0.2A (this in itself is strange as I measured 0.17A last time). This is a fixed drain on the battery. If I switch the fridge off completely it drops to 0.12A which indicates that the fridge igniter and the LED take 0.08A and the PDU, which I can’t turn off takes, 0.12A.
Over a week this is a severe drain – its 13AH for the fridge igniter and 20AH for the PDU.
Now festivals tend to be in summer, so I would not envisage turning the lights on till about 8pm. We enjoy ourselves at these events and will be out at least 5 nights. We go to bed around 1am, so lights are on maybe 5 hours per night for two nights and 1 hour for five nights. That’s 15 hours. But we may be sat outside with the awning light on for a couple of nights. So here is the calculation on the rough estimate.
As I said before we enjoy ourselves at these events and are not likely to sit around playing on tablets or PCs or watching TV, BUT they will be used modestly. Assuming they are fully charged when we set out, most will just need a single charge (probably in the form of a few top ups). Here is the calculation.
|Charges Per Week||AH|
- Fridge Igniter 13AH
- Control Panel 20AH
- Lights 15AH
- Technology 14AH
- TOTAL 62AH
The 70AH battery ain’t gonna make it.
If I use the BANNER calculation I need 62AH x 1.7(safety margin) or a 105AH Battery
BUT, that Control Panel is really taking the biggest single share and I don’t need it. I’ll add a switch to switch it off when I’m not using it (I can’t use the isolator as it will also switch off the fridge re-igniter) and I reduce the power used to 42AH.A 70AH .battery could do it
But I’m not sure of the history of my battery – I let it drop to 7.4V once, only for a few hours, but it may still be degraded. And, realistically there is not enough safety margin there to stop me worrying.
It says POWER MAX but its not listed on the Power Max website. It came with the van and is quite widely available in the UK, The batteries on the Powermax website do not have labels like this and the suppliers do not provide a data sheet. Is it really a PowerMax battery?
Basically, its working fine for the modest uses I’m putting it to but the discussion about choice of battery below explains why I don’t trust it.
I have ascertained that, if I have a good battery, I still don’t need solar panels even if I am parked up for a week.
Going for a week or more on a single battery and no solar panels seems to be against most of the advice in forums and magazines. And these are written by experienced motorhome owners. Why the discrepancy?
Some (most even?) of these folk will have bigger vans than I have with multiple rooms and thus more lighting and heating. Most will not have switched to LED lighting. Many using inverters, (which are not very efficient) to power TVs, PVRs, and even hair driers and microwaves. Some have heating systems that depend on an electric fan. Some spend all night in the van watching TV. Some have offspring who use the computer all day long.
My van lifestyle uses much less electric power than that. I have only one room (plus a loo and shower). I only use LED lighting. I rarely use the inverter, and have no real interest in watching TV when we are away, other than the odd news program.
Leisure Battery Issues
Its not uncommon for motorhome users to fit two 110AH batteries and a roof-full of solar panels and be happy that they can manage a week end away in summer. Their batteries may be heavily sulphated and only providing only a fraction of their original capacity but the owners never know and it doesn’t really matter to them.
The batteries may not even be “proper” leisure batteries. A test by the caravan club showed that only 2 out of 9 batteries tested were actually leisure batteries and the remainder were starter batteries with leisure battery labels.
It is so easy in a modern motorhome to completely flatten a battery and thus drastically reduce it’s performance. Continuous drain can be as high as an amp and this will flatten a battery in a few days.
Solar panels are of little help in the winter. There is not much sun but lots of dead leaves, and possibly snow to reduce or even stop the solar panels output.
In fact a van left for a few weeks in late autumn or early spring may have its batteries virtually flattened every night and charged up partially the next day. Start the van and the battery will quickly charge up fully and all looks OK.
The severely weakened batteries will soldier on and still provide enough power in the summer to last overnight until the solar panels start generating power, so the user will be unaware his batteries are severely degraded. They are still good enough for his needs
My battery will get welI used but not stressed. I’ll stand by my calculations.
Choosing a leisure battery
Batteries have different capacities at different drain currents. They are usually rated at a 5Hr, 10 hr, 20hr and 100hr. In my case average current drawn is about 2A with just the lights – It is much higher if I was charging everything at once, but why would I? The PC will take about 5A, but only for 90 minutes or so. The rest of the electronics will take under 2A total. With a 110AH battery the 20hr rating is 5.5A. the 100hr rating is 1.1A. I’ll be closer to the 100hr rating but I’ll use the 20hr rate to give me a safety margin.
The leisure battery market is a minefield. A recent Caravan club investigation showed that many (probably the vast majority of) batteries sold as leisure batteries are in fact starter batteries. There is a difference. A leisure battery will not happily provide the huge surge of current that the started need particularly when its cold. A starter battery will not be happy discharging below around 70% and will begin to irreversibly degrade if it does. Think about it – it starts the car with a huge current – maybe 800+ Amps for around 5 seconds. That’s about 1AH, from, maybe, an 100AH battery. Then the alternator pumps power back into the battery at around 20 amps or more. It charged up again in a minute or so. Leave you side lights on for a day and you will take around 24W or 2 Amps over say 10 hours – that’s 20AH. You have only discharged the battery to 75% so it should be fine, but its still only rated at around 40 cycles or thereabouts so don’t make a habit of it.
The leisure battery does not need to supply huge surges in current, But it does need to supply current over a long time. A 100AH leisure battery should be able to supply around 50AH before a charge, and do it 400+ times.
My van is quite heavily used. We have spent over half our time in it in the last 5 months.But the battery now (since doing the mods listed in part 1) has an easy time. Its average discharge before recharge is only around 10%, but that could be 100+ times a year. In addition it will get around 20% discharge a dozen or so times and 40% maybe three times a year. Now I want my battery to last at least five years. So thats 500 cycles by 10%, 60 cycles at 20% and 15 cycles at 40%. A starter battery might manage that, any real leisure battery should laugh it off, and a good one may last twice as long.
What I would really like are datasheets (I am an engineer – I trust datasheets, not salesmen) but a fairly long search on the web has thrown up very little in the form of hard data. The Caravan club test showed that Varta, and Banner batteries were real leisure batteries. Exide also may be OK but the CC could not fine a battery to test. I have also found that Bosch make batteries with defined cycle count and DOD (Depth of Discharge) values. Also Trojans batteries are all real deep cycle, as thats all they make.
AGM – The LAD115 looks like the best. its rated to 800 cycles at 50% DOD but its £230. How long would it take me to ramp up 800 cycles? My battery is only going to get discharged by 50% a few times a year!
Flooded – The LDF90 is rated at “up to twice the cyclic stability of conventional flooded batteries” – up to 200cycles @ 50% DOD its £80. I hate the phrase “up to”. Does this mean it may only be 100, or 50, but it definitely won’t be more than 200. Its a weasel expression and does not inspire confidence. Its a Dual purpose battery – I don’t thing they make any real leisure batteries now other than the expensive AGM ones
The 813010 looks like a real leisure battery but its not on Varta’s own site – probably old stock.
The 120AH Energy Bull 959 01 looks good but I can’t find any specifications about number of cycles (except 3x a starter battery but they don’t say what a starter battery is!) The Varta spec would imply 100cycles, but its a different supplier). It would cost around £142 from the web inc delivery. Banner do have a really good reputation though
The Bosch L4 018 (110AH) and L4 020 (125AH) look good “Exceptionally high cycle stability – 300 to 400 charge and
The 018 is £106 with free delivery
I can’t find a supplier for the 020
Many suppliers advertise the The Bosch 679 (strangely they all seem to use a photo of the L4 018!) but its not on the Bosch website and there are no datasheets – so what is it? Its a slightly different size to the L4. Is it a rebadged starter battery?
I suspect that Bosch (owned by Johnsons who also own Varta) are selling the rights to use the names to other manufacturers. So are suppliers selling Bosch Batteries or just Bosch Labels?
ER 550 looks OK but theirdata sheetis silly. It implies 250 cycles at 50% reducing at lower discharge rates. Do I want to get a battery from a company who prints this rubbish.
Varta seem to be all expensive AGM batteries now – and they have dodgy specs
Bosch seem to be getting their batteries elsewhere.
Exide have silly specs
Banner and Trojan both still seem to be making flooded deep cycle batteries.
It comes down to the Banner 120AH Energy Bull 959 01 the 105AH Trojan 27MTX or the 115AH Trojan 27MTH
Any of the batteries should last well if cycled down by only 50% but could do the occasional 80%.
A week at a festival should be no problem with any of these batteries and they could probably to a fortnight at a pinch. If I really get pushed (I doubt I ever would) then half an hour with the engine running will put about an extra 3 days of power back into it. That should cost me about 35p, and if I pick my time right it should not upset the neighbours too much.
I didn’t want the battery delivered, I wanted to pick it up. Web suppliers of Trojan batteries ignored my emails, and local suppliers wanted £190 for the 27MTX. SO I bought the Banner 120AH Energy Bull 95901 from APDin Cirencester for £110.46. A good price in my opinion and extremely fast service – they didn’t have it in but it arrived next day. Its fitted now – no issues. There is not a vent hose – I need to get that sorted and also arrange something to keep it secure in the battery box.
I also need to change the electrics a bit more – More power technicalities