Infrequently Driving a PHEV

[DangerDoom]

Apologies if there was a previous thread on this... I looked but didn't find one.

Is there any guidance on how frequently a PHEV should be driven? The vehicle in question is a Mitsubishi Outlander PHEV. The car will be in a garage and can be plugged in. There won't be a reason to drive it for at least 2 or 3 months.

Should the Outlander be left plugged in for that kind of timeframe or would it be best to fully charge the battery and then disconnect?
Should the car be driven every week, every two weeks, every three weeks? If so, is it a good idea to make sure the petrol engine is used for a while?
Any other maintenance points to consider?

Appreciate any advice.

[gangzoom]

Is it your car? and how long are you planning on keeping it?

The main problem with leaving a battery fully charged is degradation. Keeping a battery at 100% or at 0% for pro-longed periods speeds up the rate of degradation. The recommendation from manufactures I believe is to try and keep the charge at below 80% but above 20%. So I suppose you could charge it up to 80% and leave it there.

If you only keeping the car for 2-3 years battery degradation is probably less of a concern, since your be moving the car on.

[Adamski69]

Quick call to a Mitsubishi dealer for advice perhaps...?

[jkh112]

If you are doing this regularly then it would be good to speak to Mitsubishi etc. If this is a one off event then just leave it plugged in. I would rather come back to a charged battery than a flat one with all the problems that may bring.

[anonymous-user]

Is there a discharge when it's just stood there, which means it can't just be charged up and left? If so, what about putting a timer in the charging circuit so that it gets a boost for a short time daily, or even weekly?

Not the same I know but I leave my Caterham unused for long periods over winter and I have it connected to a battery 'conditioner' which comes on for a short time every afternoon.

[blueacid]

Maybe it's worth getting a 7 day timer plug? Give it a few hours per week but not leaving it plugged in permanently?

Or is there a way to disconnect the battery pack to prevent parasitic loads from draining it? It shouldn't self-discharge by a tremendous amount i'd think?

[jkh112]

I think using timer plugs on smart chargers can cause more harm than good. The smart chargers are designed to be left live for long periods and when the battery is near fully charged it ramps down the charge level and balances the cells etc. Some of them also turn on at near full power for the intial period when electricity is first applied. If a timer plug keeps switching it on and off it may not be able to do the final balancing part of the charge.
I leave a trickle charger attached to my bike for the entire winter period and the battery has lasted many years, I have also done similar for months on end on my car whilst working away as a modern smart charger will not over charge like old fashioned units may have done. Similarly I would be happier leaving the charger unit to look after my PHEV battery for a long period rather than keep switching it on and off with a timer unit.

[anonymous-user]

jkh112 said:

I think using timer plugs on smart chargers can cause more harm than good. The smart chargers are designed to be left live for long periods and when the battery is near fully charged it ramps down the charge level and balances the cells etc. Some of them also turn on at near full power for the intial period when electricity is first applied. If a timer plug keeps switching it on and off it may not be able to do the final balancing part of the charge.
I leave a trickle charger attached to my bike for the entire winter period and the battery has lasted many years, I have also done similar for months on end on my car whilst working away as a modern smart charger will not over charge like old fashioned units may have done. Similarly I would be happier leaving the charger unit to look after my PHEV battery for a long period rather than keep switching it on and off with a timer unit.

I understand what you are saying but the charger I use doesn't charge at high power unless it needs to, though I don't know about others.

Incidentally, Yuasa for one advise against leaving smart chargers on for long periods, though they are talking quite a few weeks, not days. They say there is a risk of sulphation if one does that and recommend 'exercising' the battery by disconnecting for short periods.

I haven't had any issues so far but I think I'll make a compromise and start leaving it connected for a few weeks and then disconnecting it for a day or two.......

[Jonny_]

gangzoom said:

Is it your car? and how long are you planning on keeping it?

The main problem with leaving a battery fully charged is degradation. Keeping a battery at 100% or at 0% for pro-longed periods speeds up the rate of degradation. The recommendation from manufactures I believe is to try and keep the charge at below 80% but above 20%. So I suppose you could charge it up to 80% and leave it there.

If you only keeping the car for 2-3 years battery degradation is probably less of a concern, since your be moving the car on.

This is the reason that Toyota hybrids don't actually use all the battery capacity; when the display shows "full" the battery is only 80% charged in reality, "empty" is actually 40% charged, and in normal running the car aims to keep the state of charge at around 70%. By never fully charging or discharging the service life of the battery is much improved, albeit at the expense of outright capacity.

While I don't know for certain, I would expect that the Mitsubishi, and pretty much all other hybrids and EVs, use a similar regime to minimise battery degradation.

My own view would be that leaving the charger permanently powered up shouldn't harm the battery as it will aim to maintain a safe state of charge, rather than holding it at 100% and hastening degradation. However, the charger will always draw some power whether or not it is actually supplying charging current to the battery, so it could be worthwhile using a timer to run the charger for perhaps a only couple of hours every few days. The battery self-discharge shouldn't be fast enough to need more than an occasional brief top-up.

[Rostfritt]

Jonny_ said:

This is the reason that Toyota hybrids don't actually use all the battery capacity; when the display shows "full" the battery is only 80% charged in reality, "empty" is actually 40% charged, and in normal running the car aims to keep the state of charge at around 70%. By never fully charging or discharging the service life of the battery is much improved, albeit at the expense of outright capacity.

While I don't know for certain, I would expect that the Mitsubishi, and pretty much all other hybrids and EVs, use a similar regime to minimise battery degradation.

That only really leaves you 40% of the capacity to play with which is pretty rubbish. Assuming they are lithium ion batteries like a laptop, they can be quite resilient. My laptop was permanently plugged in for the first year of its life then used pretty much from full to empty for the next 4 years and has barely lost any battery. Are the Toyota ones using lead acid batteries?

[Jonny_]

Rostfritt said:

That only really leaves you 40% of the capacity to play with which is pretty rubbish. Assuming they are lithium ion batteries like a laptop, they can be quite resilient. My laptop was permanently plugged in for the first year of its life then used pretty much from full to empty for the next 4 years and has barely lost any battery. Are the Toyota ones using lead acid batteries?

In a way it is, but the charging regime has been designed such that you will always have that 40% usable capacity for the expected lifetime of the car - at a guess around ten years or so. I suppose it's the analogous to the American cars of the 1980s, whose big V8 engines produced no more power than a decent European four pot, but had a much longer service life through being less mechanically stressed.

The figures I have relate to the Gen 3 Prius, and to the Auris hybrid (like wot I have), both of which use NiMh batteries rather than lithium. The official line from Toyota is that the NiMh batteries are used for reasons of durability and long term reliability, although I would imagine cost is a significant factor as well. Also I reckon that for hybrid vehicles the outright capacity is less of a concern than it would be for an EV, as the vehicle range isn't solely dependent upon the battery pack. As I understand it the Gen 4 Prius on sale next year has NiMh as standard and Li-Ion if you go for the Eco version, at extra cost, naturally.

Lithium batteries are more tolerant of deep discharge than nickel metal and so more of the stated capacity can be used without damaging the battery, although they still won't put up with being completely drained. This is one reason they perform better in power tools despite having similar voltage and capacity ratings; e.g. an 18v 3Ah lithium battery drill will drill more holes on a charge than an 18v 3Ah NiMh drill of the same power output. Downsides are that lithium cells are very intolerant of overcharge, overdischarge or reverse charging (when there is one weak cell in a series pack), which makes them more of a safety hazard and necessitates a complex charging system that can monitor each individual cell.

(If that hasn't bored you half to death then, like me, you ought to get out more...! )

[JonnyVTEC]

Rostfritt said:

That only really leaves you 40% of the capacity to play with which is pretty rubbish. Assuming they are lithium ion batteries like a laptop, they can be quite resilient. My laptop was permanently plugged in for the first year of its life then used pretty much from full to empty for the next 4 years and has barely lost any battery. Are the Toyota ones using lead acid batteries?

Does you laptop discharge 100A of current?

[Rostfritt]

JonnyVTEC said:

Does you laptop discharge 100A of current?

Feels like it does sometimes. Current drawing 1145mA.