# How does a manufacturer determine the warranty for the battery?

I was looking at replacement batteries for my car (Honda Insight). The dealership was selling a battery that had a 100 month limited warranty. The next highest warranteed battery from Autozone, Pepboys, Oreilly, etc. was for 60 months.

The price difference is about \$50. I'm trying to figure out why or how did the Honda design their battery such that it lasts almost twice as long as the next closest battery? I just thought the dealership marked up their battery but if it lasts twice as long, I'd be foolish not to buy their battery.

• They don't last longer. The higher price is just a longer insurance policy, and they prorate the warranty, i.e. they only compensate you for the time not used on the returned battery... Oct 20, 2019 at 22:42
• @JimmyFix-it - Most batteries last around 60 months ... give or take. If they are going to warranty them for 100 months, they have to be doing something different or they'd lose their shirts on returns, even if they are prorated. Oct 20, 2019 at 23:01
• Judging by UK prices, a \$50 premium is about half the retail cost of a "bog standard" battery, so you are just paying for your potential replacement under warranty up front - and most likely you won't be keeping the car 8 years anyway, and the guarantee might not be transferable if you sell it. There are lots of ways for Honda to win here. Oct 20, 2019 at 23:32
• "how did the Honda design their battery such that it lasts almost twice as long"... psst... 60-month warranty vs 100-month warranty is 66% longer, not "almost twice". (100-60 = 40mon. 40/60 = .6667 = 66.7%) Generally, you can round to get a good approximation, but in this case, your rounding is actually pretty far off and can really throw off your ROI calculation. Oct 21, 2019 at 13:34
• This is primarily a financial calculation. In order to do the calculations, we need either the actual costs of the two different batteries (which gives us the actual difference), or the difference in cost stated as a percentage of the full cost of one of the batteries (and which one it is a percentage of specified). For this, the actual costs are preferred, as it removes any issue wrt. how you calculated the percentage. Without that information, we have to guess. We can do a reasonable guess, based on local prices for batteries, but it won't be accurate. Also need: actual warranty terms. Oct 21, 2019 at 16:08

All batteries last about the same amount of time, given the same climate and average use. I'm betting the dealership uses a large battery warranty to lure you in to other services, like a "loss leader". It's also common with free oil changes when you buy a car at a dealership. They lose money on the oil change but plan on you buying other stuff at a premium.

• Not in Arizona. You need to replace your battery about every 24 months. It's the heat, I assume. Some battery warranties will replace the battery for a specific period of time and then pro-rate after. I lived in the Seattle, Washington area for 25 years before moving to AZ and I think I only replaced 1 or two batteries. Oct 21, 2019 at 15:22
• I lived in Iowa almost 40 years and drove for over 20 of them. I replaced batteries about every 5 years, even when the warranty was 7 years. The extreme cold of -45F and high of +110F can destroy a battery real quickly. I've seen batteries burst when they freeze. Even -20F for an extended period can destroy a battery, if the car isn't run long enough to fully thaw the battery at least 2x a day. Oct 22, 2019 at 16:41

They may make 100-months guaranteed batteries with higher real capacity than 60-months ones. Higher capacity means that harmful events like overcurrent or deep discharge are less likely to happen, and that a battery still works fine after losing some of its original capacity, because the remaining capacity is still enough to reliably start the car.

I would rather get a 60-months guaranteed battery with 20%-30% more capacity than required, provided you can fit that battery in your car. I bet the price difference w.r.t. a normal 60-months battery will be less than \$50.

I once had to change a battery in a bigger car, and donated my old battery to a friend which had a smaller car those battery was dying too. My old battery lasted another 5 years in that smaller car.

• Concur - I put a ridiculously over-sized battery into my car, over 12 years ago and its still going strong. Why oversized? Because it fitted in the battery tray. Oct 22, 2019 at 0:39

Don't mistake the length of a battery's warranty with how long a battery will 'last' - it's just a warranty, not a guarantee of performance.

So here's how it works: you buy a battery for \$100 with a 60 month warranty. In 30 months, it dies.

You go back to where you purchased the battery, and you will pay \$50 for a new battery - that's called a 'proration'.

The theory is that when you purchased the original battery (or original warranty) you were owed 60 months of starting. The battery only provided 30 months, so they owe you 30 months. That leaves extra 30-month on the new battery that you now need to pay for.

I can't speak for all battery brands, but I used to sell Excide, Motorcraft (Ford), and AC Delco.

Each battery had a month/year code as part of the labels. The month/year code would be used to calculate the proration (e.g. how much the, if any, the customer would pay for a new battery).

The obvious question here is: what if the battery was sitting on the shelf for 12-month, would that mean the customer loosed 12-months of warranty? No - each moth the battery vendors would swap-out the batteries in the store so that they were always 'fresh'

This sounds like a lot of work, but, going way back, if you bought a new battery, you would have to wait for it to be charged-up before you use it* - this way the batteries are good to right off the shelf.

*for the most part motorcycle batteries are still this way (you have to add the electrolyte and change them before used)

The people in the sales/advertising department decide what will sell best. Long ago, the advertising people at Amoco picked some random long life number. To maintain company reputation , about any battery was replaced if a customer complained. When batteries failed and warrentee costs went up , some manager decided that some objective testing should be done, after the fact. The research department conducted a pretty extensive program of battery testing. As I remember some specifications were written for batteries and certain manufactures were approved to produce "Amoco" batteries. I did not work on the program, only witnessed some of it ; some "fast drain tests" were pretty impressive with large resistance coils glowing red hot. Also keep in mind that batteries were an insignificant part of Amoco's business , it was more about reputation. Things are likely different at an auto supply store where battery sales may be important.

It's common to think of equipment failures as a linear equation where failure rate increases over time. This is not aligned with reality, however. A common way to model failure rates is the use of the 'bathtub curve'

My personal experience with batter failures has been with 2 Hondas. One went more than 6 years (72 months) and the other lasted over 12 (144 months.) I'm therefore a little dubious about the idea that all batteries last about 60 months. The reality is that once something lasts through the 'infant mortality' period, it's very likely to last a relatively long time. Replacing things when they reach their average (mean) life expectancy is misguided.

When evaluating the length of these warranties, the rational choice is pick the term to end prior to the 'wear out' period. The chance your battery dies right around the the end of the warranty period is pretty unlikely.

• IME, with the extreme weather in Iowa, batteries last around 5 years and if you got 7 years you were very lucky. I've had a total of 4 cars over 20+ years (2 for over 10 years each, owning them simultaneously), as well as helping maintain my parents cars. With a temp range of 150F between winter and summer, the batteries get both extreme heat and cold. Living in a mild weather area will get you a longer battery life, but that doesn't translate to other areas. Oct 22, 2019 at 16:51
• @computercarguy I'm not sure I would call Buffalo NY a mild weather area but it doesn't get much below 0F. Seven years was for a car in Virginia. 12+ years for Buffalo. What brand of battery? The question was specifically about Honda and these were both Hondas. Oct 22, 2019 at 18:36
• From what I see, Buffalo has a temp range of only about 60F, so that mild to me. Brands deal with heat and, separately, cold very differently from other brands. Even different quality level within brands handle them differently. My last winter in Iowa caused a retail battery shortage, due to replacements needed, and the stores even over stocked more than usual. I asked because it took several stops to find a battery for myself, after a week of -20F and below. IME, weather can have massive effect on battery lifespan, regardless of brand. Oct 22, 2019 at 18:57
• @computercarguy I've seen the mercury drop to below -10F and it can get up to 90F. Not sure how that is a 60 degree range. I would call that 100. I definitely agree weather makes a big difference and I think we both agree that this is more complicated than "all batteries last the same amount of time: 5 years." Oct 22, 2019 at 19:06
• I went off a weather site that showed 20F to 80F. That might have just been for this past year, IDK, so it could well be off. Oct 22, 2019 at 20:00