While writing a forum post on proper lithium-ion battery care, I started wondering whether the proper term for recharging them while still fairly full is called topping up or topping off.
Perhaps both are accepted?

  • 4
    Top off is my usage. I don't think I've ever heard top up.
    – user21497
    Commented Oct 21, 2012 at 7:37
  • 7
    Mine is the exact opposite. BrE v. AmE again? Commented Oct 21, 2012 at 8:00
  • 3
    I would say 'recharge', but if I had to use one of the OPs suggestions I would use top up. Top off sounds like adding to a problem - "I forgot my phone, then the car broke down, and to top it off it started raining". Commented Oct 21, 2012 at 8:52
  • @RoaringFish: Well, recharging might indicate a low charge level at the start of a charging cycle, whereas topping up/off indicates that the battery already had quite a high charge level to begin with. (E.g.: NiMH batteries should generally be recharged when nearly depleted, not be topped up/off, while lithium-ion batteries can be topped up/off safely.)
    – oKtosiTe
    Commented Oct 21, 2012 at 12:09
  • @oKtosiTe - Fully cycling either battery chemistry is bad for it.
    – Fake Name
    Commented Oct 21, 2012 at 13:00

3 Answers 3


Either one is acceptable.

Both are metaphors from filling containers with liquids -- whatever you may have been taught, electricity is not a liquid, but it often seems to behave in similar ways, and of course there were no native words for electric phenomena until it was discovered, so metaphors are inevitable. (Much the same thing is true of computers, for the same reasons.)

Both are phrasal verbs. One uses the common completive up particle (burn up 'burn completely', fix up 'fix completely').

The other has a usage of off that refers to the fact that open containers of liquids can overflow their top when overfilled -- this is the source of the causative verb to top 'cause (a vessel) to become full (of liquid)' -- plus the off that occurs in run off 'overflow (of liquid)'.

So top up means 'fill completely' and top off means the same thing; both indicate at least a chance of overflow in an open vessel. And which one gets used is largely a matter of personal or occasionally local taste. There's no semantic difference.

  • 2
    No real semantic difference, but I have the distinct impression there's a significant UK/US split favouring top up/off respectively. I think Brits normally only use top off where there's an element of flamboyantly finishing some elaborate/drawn-out procedure. Commented Oct 21, 2012 at 12:28
  • @FumbleFingers ...like the topping-off ceremony to mark the end of construction of a building.
    – DaveP
    Commented Oct 21, 2012 at 13:04
  • Yes, Americans, too. To top it all off, we will have fireworks after dinner. But never "To top it all up". Commented Oct 21, 2012 at 13:28
  • @DaveP,John: Well, I won't bother posting a "UK-specific" answer, but assuming other answers/comments are correct in saying it's unremarkable for Americans to top off fuel tanks/batteries/etc. I'm increasingly feeling there's a significant difference there. In BrE, top off almost always implies end/complete something with a "flourish". Commented Oct 21, 2012 at 13:39
  • 1
    @FumbleFingers: What, fireworks isn't enough flourish? Commented Oct 21, 2012 at 13:57

When you fill your car with gasoline it is common to "top off" the tank by adding a little more after the pump automatically shuts off. People use the same language when referring to a charge on a battery.


Does one top up or top off rechargeable batteries?

The answer is probably neither. No doubt by "rechargeable batteries" you mean the small batteries we use in electric toys etc.

We Charge lithium-ion batteries

Note "Big" lithium-ion batteries are normally not fully charged, this is to extend the cycle life of the batteries. Therefore they are not topped off they are just charged.

Industrial devices, such as the EV, typically limit the charge to 85% and discharge to 25%, or 60 percent energy usability, to prolong battery Battery University Group

The expressions actually come from a time when Lead-acid standby storage batteries had to have a whole room to contain them. And I don't mean some smallish cupboard-like room that many office servers are kept in.

Normally a Lead-acid standby storage battery is kept topped off by a float charge which does not damage the battery and maintains it at full charge. However, if the battery is ever called upon "to do its job" the battery charge level will drop. The voltage level a charger should supply in case of charging a discharged battery is higher than that for the float (top off) charge. The battery should be disconnected from the rapid charge voltage, once it is fully charged (Topped up) or it would be damaged.

The comment by MANIKANDANCHELLAKKAN in this article describes charging requirements for Lead-acid standby storage batteries Battery charger

  • 1
    "No doubt by "rechargeable batteries" you mean the small batteries we use in electric toys etc" - Why do you think that? The question mentions lithium-ion batteries, which come in a variety of sizes and are used in a bunch of products that aren't toys (as well as in toys). A Tesla car battery isn't small.
    – nnnnnn
    Commented Sep 9, 2021 at 5:45
  • @nnnnnn If we're talking Tesla, Charging Tesla batteries is complicated. They are never fully charged. Luckily, we just stick the plug in the box. There is a huge difference in cycle life between a 4.2V/cell “fully charged”) Tesla never top off their batteries and run at max 95 percent of full charge (4.15V/cell charge). For this reduction of initial capacity (5 percent), the batteries last a whole lot longer. Understanding this tradeoff, Tesla Motors has decided to limit the maximum charge of its cells to 4.15 volts, taking an initial 5 percent range hit to maximize lifetime of the pack.
    – Brad
    Commented Sep 9, 2021 at 6:58
  • The concept of "topping up" still applies to Tesla batteries. The maximum 95% charge you refer to is effectively fully charged from the driver's point of view, and if the current charge is, say, 5-10% below that the driver might want to top it up.
    – nnnnnn
    Commented Sep 10, 2021 at 4:36
  • Now you are being pedantic
    – Brad
    Commented Sep 10, 2021 at 8:55

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