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After adventures with dead battery, jump starts, and headaches, I just replaced my car battery (it was only 6 yrs old.. :( ). I am considering a portable booster pack to keep in the car, and had a question.

When purchasing my booster pack, am I better off getting a higher peak amp rating, OR, total Ah? any opinions?

details:

  • 2014 Rav 4, my stock battery had 550 CCA rating, new battery has 640 CCA rating.
  • I see one LiOn battery pack rated at 700A peak, 18Ah.
  • I see another LiOn battery pack, rated at 2000A peak, but only 5Ah.
  • variants in between..

All other things considered equal (ignoring size, etc etc.) it seems to me that I should go with the longer Ah so that I can maintain a longer crank? I've been advised by a friend (who isn't a mechanic...) to get the 2000A booster.

I do live in a very cold climate (central Canada), and use a block heater in the winter.

opinions? Thoughts? thanks!!

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If the battery pack you're looking at has a higher CCA than your regular car battery (700A far exceeds the 550CCA spec'd for your car) and it has a much larger reserve capacity, then go for it. The other one looks impressive with the 2000A rating, but doesn't give you much in the way of longevity. Also, remember, these are called booster packs or jump packs for a reason. The idea behind them is to give you enough extra battery power to get your car started when there's not enough juice in your regular battery. 700A is going to be well more than enough in most any situation to start most any automobile, plus have enough reserve to be able to do it several times. Not knowing how much they cost, I'll bet the 700A one is cheaper as well.

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  • Thanks - the point that it's 700A above my remaining battery charge is well made. And yes, the 700A one is about half price.
    – user98908
    May 13, 2020 at 21:28
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You didn't mention your engine type. It is (in general, specific cases may vary) that diesels needs way more capacity (Ah) to start. Especially in cold winter, when engine needs to preheat to start. High peak cranking Amps (CCA) will be beneficial for big engines (like V8 etc.) where you need so much power to crank engine and small booster pack will fry itself. But, since there is not much difference between your battery CCA and booster pack's CCA you will be fine.

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  • Thanks!! It's a 2.5L 4 cylinder engine. I think I'm going for the cheaper, higher Ah one.
    – user98908
    May 13, 2020 at 21:29
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Sometimes when dealing with basics of electricity, it's useful to consider an analogy with water.

Voltage is often considered pressure. Not particularly applicable in this, but included for completeness.

Amperage can be equated to volume of flow. Large diameter pipes with a lot of water moving through would be a high current level. In your example, it's the CCA, aka cold cranking amps. Bigger numbers means more "water flowing."

Ampere-hours, or amp-hours is how much water is in the tank.

As with water, batteries providing power have to have sufficient current (water flow) backed by sufficient duration (water in the tank) in the form of amp-hours.

There's little value in buying a high current battery if you don't need to pull 2000 amperes during starting. High current and small capacity won't help in a storage situation, as some of the capacity will drain away sitting idle. Lithium based batteries have a much lower loss per unit time and will probably last longer if proper charging is managed.

Lithium based batteries should not be fully charged on a regular basis. Eighty percent is a common figure in the electric vehicle world for the maximum charge for longevity. Our Rav4EVs have a built-in limiter to 80 percent and have an override for extra range, but the manual cautions to avoid using too frequently, for the aforementioned deterioration of lifespan. Tesla vehicles also have similar limitations, including excessive use of the Supercharger.

If you aren't going to exceed the 700 ampere current draw, your expectations are realistic. You'll get longer duration from a charge with more amp hour capacity.

Cold weather is particularly detrimental to lithium based batteries. Do not charge below freezing, as it can permanently damage the battery. Expect reduced capacity directly associated with temperature drop.

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  • Thanks for your answer. I apologize for not being fully clear - I do understand well the difference between Ah and A. My question is which is more useful from a car perspective. If my battery is 640 CCA, I'm wondering if I'll benefit from the higher peak A, or, the Ah which gives me a longer crank. Thanks!!
    – user98908
    May 12, 2020 at 23:08

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