Does repeated discharge damage the battery?

I live on the top of a hill. It is just high enough to climb up in EV mode if the battery is close to fully charged at the bottom; typically, it goes down to '2 bars' just before I turn into my drive way and the gas engine kicks in for the last half minute or so. Of course, when I leave the house in the morning, I go down the same hill and when I am down the battery is filling up again (not to 'full' because of inefficiencies but nicely charged).

So, I have taken the habit of saving gas by driving up in EV mode (at least if nobody is behind me since going uphill electrically is not exactly sporty driving).

My question is, am I penny-wise and pound-foolish? Am I saving a few ounces of gas every day (plus the satisfaction of doing something good for the planet) but doing damage to the battery on the long term? I know that the lifetime of some battery types, like lead-acid, is given (or at least strongly influenced) by the number of discharges. Is this the case for the Prius battery?

FWIW I tend to keep my cars for a long time (last one was retired at >20 years) so I will not kick down the problem to the next owner. Also, in case it makes a difference, I have a Prius V (wagon).

Thanks!

 

sorry for the double posting. I don't seem to be able to remove it.

 

By "more balanced than expected" do you mean that driving up electrically is unlikely to make a substantial difference?

 

First, thanks to all that replied.

Getting some real data is a great idea. However, I did some back-of-the-envelope calculations and my situation may not contribute much insight. Still, it may be instructive, so here it is (I am thinking aloud...). Keep in mind this is all 'order of magnitude' calculations, meaning it may well be off by a factor of two or three, but unlikely to be off by an order of magnitude (a factor of 10).

Say, my hill is a drive of about a quarter mile. The instantaneous fuel consumption reading says something like 20 MPG when I go up with the internal combustion engine. So, the whole hill uses about 1/80th of a gallon. If I do this once a day, I will use about an additional 6 gallons a year (365 * 1/80).

The bad news is that this is unlikely to be detectable. Even if I would systematically go up a whole month the hill electrically, and the next month non-electrically, the difference would be less than a half gallon over the whole month (30/80) which most likely would be in the noise.

Over the long run, say until the warranty on my battery runs out after 8 years, I would use an additional 8*6 gallons. Assuming current gas prices of $4.-/gal, this will cost me an additional $192.-, call it $200.-

Replacement cost of a battery seems to be somewhat above $2K, ten times as much. The worst case scenario is a total failure of the battery one day after 8 years, requiring me to fork out this amount. The best case is that using the battery the way I do results in no damage at all (or even some prevention of damage). Reality has to be somewhere in-between these cases.

I think the conclusion to be drawn from this is that, essentially, it does not matter. Using 6 gallons a year more or less is in the noise. Whether it does any damage to the battery or not is unknown (at least to me).

So, I am probably way overthinking this

 

Well, as I said in my original post: I go up (typically) in the evening and then go down the next morning. During the downhill portion, the battery gets charged again if I depleted it during the climb. Not to 100% but pretty much all the way. This is helped by the fact that the ICE is cold in the morning so it will kick on, so I will have to drive down the hill with the ICE running anyway. If the battery were still charged at this time, there would be no regeneration and the energy would be lost (to friction in the mechanical brakes).

Therefore, I do think that it is really "additional" gas, though not a whole lot...