I am interested in how batteries might be used on the JWST. A few questions come to mind:

  1. Does the JWST have onboard batteries?

If so,

  1. What kind of batteries are they?

  2. Are they rechargeable?

If so,

  1. How are they recharged? … from solar panels? … from reclaiming dumped energy from reaction wheels?


  1. If there are batteries in use on the JWST, what major (and/or minor) systems depend on them?

Another way of asking (5) might be, if there weren’t batteries on the JWST, what wouldn’t work??


2 Answers 2


JWST uses "ABSL™ 8s44p rechargeable Li-ion batteries", that's 8 series by 44 parallel (352 total) 18650 cells.

The particular Sony 18650 Hard Carbon (Mandrel) or HCM cell has a "nameplate capacity" of 1.5 Ah (5.4 Wh) [1][2]. Each 8s44p battery unit has a "nameplate capacity" of 66 Ah (1900 Wh).

It's unclear how many of these battery units are on JWST. ABSL parent company Enersys says this in a press release on the launch on JWST:

EnerSys was selected by Northrop Grumman in 2012 to provide ABSL™ 8s44p rechargeable Li-ion batteries with disconnect relays for Webb, and then awarded a second contract in 2018 for an additional 8s44p battery, tailored to incorporate alternate cell chemistry.

While a 2020 JWST (draft) update [3] says this about batteries:

battery change JWST


Results from recent contingency analyses indicate the amount of time to work contingencies in the event of post-launch solar array deployment (t +30 min) anomaly has fallen under 3 hours with the current ~53 AH battery (HCM Li Ion).

  • Fortunately, we procured a spare (Moli-M Li Ion) battery that was of considerably larger capacity ~106 AH – two years ago and it is ready to go. This more than double capacity will provide more that sufficient time to complete all possible contingency operations to recover the solar array.

  • For these reasons, the project has decided to switch to the space battery. GSFC Engineering Directorate and the Standing Review Board have been briefed on this decision.

It should be noted that 53 Ah is almost suspiciously 80% of 66 Ah, which is not an unreasonable "depth-of-discharge (DOD)" limit in a contingency scenario.

These sources seem to be talking about the same thing (timelines match), though they are conflicting on implied battery quantities on JWST.


  1. Pearson et al. "The Use of Small Cell Lithium-Ion Batteries for Small Satellite Applications," (2004)
  2. Troutman, J. "ABSL Performance Comparison," (2011) (slideshow)
  3. Smith, E. "JWST Update (DRAFT)," (2020) (slideshow)

Yes, the JWST has rechargeable batteries, they are recharged from the solar panels.

Using non rechargeable chemical batteries would not make sense.

The rechargeable batteries of JWST are the lithium-ion type. The batteries use the Sony 18650 hard carbon cell technology. The batteries are designed to endure spaceflight, and should sustain 18,000 charge-discharge cycles.


Without electrical power the JWST would be useless.


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