Help! What’s happening to our batteries?

[Riverbankannie]

Thank you for all your replies. We’ve now moved to a site with hook up. We can use campsites all the way back to Santander in 2 weeks although it’s a shame as there are some lovely aires in Spain that we had intended trying. When we went to bed last night the battery was on 12.4v, fridge off, nothing drawing. It was 9.7 on waking so clearly damaged beyond repair. If it’s not a daft question I presume we can just use campsites all the way home without any problems likely to occur, I must admit that speaking no Spanish and being far away from big towns or cities, we don’t really want to go off and try and get new leisure batteries while we are away.

We have been turning off our 3 way fridge on our trip without too much loss of cooling. (Our relay / fuse to prevent use when engine not running has been clicking madly)
If your chosen aire higher up inland, therefore cooler, then leaving fridge off for a while shouldn’t harm contents.

 

[Billy192]

Thank you for these replies. I wonder if lithium batteries are required before our next saunter abroad.

yep lithium are the way, i am in Javae running my 3 way on 220 off an inverter batt is 300ah and its so sunny it dips to 80% in the night but by lunch time 100%

Billy

 

[Old Gibber]

I'm assuming the 200Ah of batteries are lead acid, so you've only got about 100Ah before you're starting to damage them.

If your batteries were healthy, you should have got a few days before they started to die.

Sorry but this simply isn't true. Batteries lose their capacity due to a number of factors. Age, battery construction, storage conditions, number of charges, rate of charge, number of discharges, rate of discharge, depth of discharge, etc.

In other words the damage starts from the moment you fit them, no matter what you do to them. The rate of damage is a factor of all the above factors.

This graph shows the real relationship between depth of discharge and number of cycles (i.e. the number of times the battery is charged and discharged). As can be seen the 50% value is utterly meaningless in this context. Its a figure dreamed up by those advertising lithium batteries and falls neatly into the "lies, damned lies and statistics" category.

Draining the battery completely before charging will significantly reduce its lifespan however.

Also lets consider the worst case scenario, 80% discharge every time. That still gives a usable lifespan of 500 cycles. That's nearly 2 years worth of use discharging the battery down to that level EVERY DAY. Clearly few of us would do that unless off grid and full timing.

Finally, the number of cycles refers to the number of cycles before the battery drops to 80% of the original capacity. Obviously you can use the battery well beyond that.

 

[Hoovie]

Sorry but this simply isn't true. Batteries lose their capacity due to a number of factors. Age, battery construction, storage conditions, number of charges, rate of charge, number of discharges, rate of discharge, depth of discharge, etc.

In other words the damage starts from the moment you fit them, no matter what you do to them. The rate of damage is a factor of all the above factors.
View attachment 684261
This graph shows the real relationship between depth of discharge and number of cycles (i.e. the number of times the battery is charged and discharged). As can be seen the 50% value is utterly meaningless in this context. Its a figure dreamed up by those advertising lithium batteries and falls neatly into the "lies, damned lies and statistics" category.

Draining the battery completely before charging will significantly reduce its lifespan however.

Also lets consider the worst case scenario, 80% discharge every time. That still gives a usable lifespan of 500 cycles. That's nearly 2 years worth of use discharging the battery down to that level EVERY DAY. Clearly few of us would do that unless off grid and full timing.

Finally, the number of cycles refers to the number of cycles before the battery drops to 80% of the original capacity. Obviously you can use the battery well beyond that.

I think it is worth point out that the chart above would be for a particular type and model of battery (assuming it is not for a hypothetical battery).
Different batteries have different discharge curves, and different technologies, including different ones within the "Lead Acid" family, are different again.
Very few Standard Motorhome Fit Lead Acid Batteries have a discharge cycle of 500 at 80% discharge. This is a chart from Banner Bull showing off their battery cycles. It is presented differently with State of Discharge on the Y Axis and Cycles on the X, but for their standard battery, at 50% DoD, they claim ~250 cycles and at 80% DoD they quote just 150, a far cry from the 500 in the previous chart. (and they claim a "conventional" battery would have just 40 cycles at 80% DoD (not sure what they mean by "conventional". maybe a starter battery used as a Leisure one?)

I am not saying the earlier chart is wrong, but the chance of it pertaining to any specific battery that a forum member reading it is extremely remote.

As far as the oft quoted mantra of "don't go below 50% or you will damage the battery", there is some truth in this for basic Lead Acid batteries and not just down to reducing the charge cycle count. You can do irreversible damage if you take a battery down to far which can result in being unable to recharge fully, so if you do have cheap batteries like the typical popular Banner Bull SLA ones, it is best to avoid dropping past half way.

 

[autorouter]

This graph shows the real relationship between depth of discharge and number of cycles (i.e. the number of times the battery is charged and discharged). As can be seen the 50% value is utterly meaningless in this context. Its a figure dreamed up by those advertising lithium batteries and falls neatly into the "lies, damned lies and statistics" category.

Draining the battery completely before charging will significantly reduce its lifespan however.

Also lets consider the worst case scenario, 80% discharge every time. That still gives a usable lifespan of 500 cycles. That's nearly 2 years worth of use discharging the battery down to that level EVERY DAY. Clearly few of us would do that unless off grid and full timing.

So let's take an example. Suppose you happen to use exactly 80Ah every day.

Scenario 1. A single 100Ah battery, using 80Ah, would discharge to the 80% level, According to your graph, it would last 500 days. At the end of that time, you could scrap it and buy another. It would also last 500 days. So two batteries would last for 1000 days of use, and four batteries would last 2000 days of use.

Scenario 2.Two 100Ah batteries, using 80Ah, would discharge to the 40% level. According to your graph, they would last 1300 days. So two batteries would last for 1300 days, and four batteries would last for 2600 days.

Scenario 3, Four 100Ah batteries, using 80Ah, would discharge to the 20% level. According to your graph, they would last 2900 days.

So keeping the discharge level to 40% instead of 80% gives a big improvement (2600 days instead of 2000 days).

However keeping the discharge level to 20% instead of 40% doesn't give such a big improvement (2900 days instead of 2600 days).

This kind of calculation is the basis of the idea that the 50% discharge level is a good compromise between good battery cycles carrying the weight of multiple batteries. Obviously if you have very restricted payload then your optimum point will shift, and you may prefer to have fewer/smaller batteries and replace more often.

The point is, there is definitely a logical basis to the '50% discharge' rule of thumb.

^{_{Subscribers  do not see these advertisements}}

 

[Old Gibber]

The point is, there is definitely a logical basis to the '50% discharge' rule of thumb.

As a rough rule of thumb, probably OK, but the point I was making is that it is incorrect to say discharging below 50% damages the battery. Every time you discharge it to any level you damage the battery.

In any case the reality is most of us don't discharge a battery to the same level every time we use it, and the above graph then gives plenty of leeway. Personally I work on the basis of a battery lasting 5 years, a rule that has worked for me for many years. OK batteries do fail well before this for many reasons, but they also can last longer too. I've used my motorhome for 96 days this year, and out of that, I've probably been off grid for less than 20 of them.

 

[Old Gibber]

As far as the oft quoted mantra of "don't go below 50% or you will damage the battery", there is some truth in this for basic Lead Acid batteries and not just down to reducing the charge cycle count. You can do irreversible damage if you take a battery down to far which can result in being unable to recharge fully, so if you do have cheap batteries like the typical popular Banner Bull SLA ones, it is best to avoid dropping past half way.

While I agree different batteries will have different graphs, those graphs of yours do illustrate that 50% is not a magic figure, its a continuum. Take the cheapo Energy Bull, discharge it down to 40% and you get 350 cycles. Discharge it down to 50% and you get about 275 cycles, down to 40% and you get 210 cycles.

I think that graph merely shows it pays to buy a better quality battery, or go for Gel or AGM.

 

[Hoovie]

While I agree different batteries will have different graphs, those graphs of yours do illustrate that 50% is not a magic figure, its a continuum. Take the cheapo Energy Bull, discharge it down to 40% and you get 350 cycles. Discharge it down to 50% and you get about 275 cycles, down to 40% and you get 210 cycles.

I think that graph merely shows it pays to buy a better quality battery, or go for Gel or AGM.

Not my graphs. And I make no claim for their accuracy

 

[Minxy]

This ad has just appeared on classifieds, any good?

Exide ES900 Gel Leisure Batteries x 3

Here we have 3 Exide ES900 Gel batteries (80AH each) just removed from a new van delivered in early September of this year. Reason for their removal was to increase capacity with Lithium, and upgrade the charging system in the van. In use for the one...

www.motorhomefun.co.uk

 

[BooBooKing]

Look good but we are still in Spain so sadly not for us.

^{_{Subscribers  do not see these advertisements}}

 

[Minxy]

Look good but we are still in Spain so sadly not for us.

You could always arrange to get them when you arrive back in the UK.

 

[Richard n Ann]

You could always arrange to get them when you arrive back in the UK.

Yes, I'd be buying them