Short answer: a 750mAh LP-E17 loses capacity a little at a time in normal use and does not fall to zero on a particular day. The usual industry rule of thumb is that a lithium-ion battery retains about 80% of its factory capacity after 300 to 500 full cycles, which at two or three charges a week works out to one or two years. So the question is not how long the battery has been in service but whether it still covers one of your shoots.
What follows separates the mechanism of the loss, the checks you can run yourself, and the point at which replacement makes sense. Every figure here is a range or a rule of thumb; for a specific battery, only your body and your shooting load can give the answer.
Where the loss actually happens
The capacity of a lithium-ion cell comes from lithium ions that shuttle between the electrodes. With every charge and discharge, a small fraction of those ions is locked out of circulation by side reactions: the SEI layer on the anode thickens, and the cathode material picks up minor structural damage. Those ions never return, and the visible result is a capacity that shrinks bit by bit.
Internal resistance deserves more attention than capacity. Rising resistance does not only mean the battery holds less; it means the battery cannot deliver what it holds. Under high current the voltage drop across that resistance pulls the terminal voltage down to the body’s cut-off early, so the body reports empty. This explains why some old batteries charge to full, then lose a bar after a few dozen frames.
Temperature is an accelerant. Batteries stored somewhere warm over the long term, such as a car in summer, next to a radiator or beside a laptop vent, fade noticeably faster than batteries kept at room temperature. This hurts a small battery like the 750mAh particularly, because its margin was thin to begin with.
Three checks you can run yourself
- Establish a baseline. When a new battery arrives, record one run in a fixed way: same body, same lens, same framing method, for example screen framing throughout with stabilization on. Shoot until the camera shuts itself down and note the approximate frame count or duration. That figure is the battery’s factory baseline.
- Retest periodically. Every three or four months, repeat the test in exactly the same way. Charge it fully, then let it rest for an hour or two before starting, so residual warmth does not skew the result.
- Work out the ratio. Divide the retest figure by the baseline. Around 80% is normal aging; below 60% is clear degradation and time to think about a replacement.
This needs no instruments. The error comes mainly from variation in shooting load, so keep the retest in the same kind of scenario, for example indoors with the same burst rhythm. If your work varies a lot, a cruder estimate works too: count how many batteries a single outing now consumes.
Three signals that mean replace it
| Signal | Typical behavior | Action |
|---|---|---|
| Usable capacity below 60% | A half day that one battery used to cover now takes two | Demote to backup, buy a new primary |
| Voltage that cannot hold | Shows full, then drops a bar or warns low after a few dozen frames | Stop using it for important work |
| Charging anomalies | Fills much faster on the LC-E17, or gets noticeably hot while charging | Stop using and stop charging immediately |
The third deserves its own emphasis. A sudden drop in charging time usually does not mean the battery has improved; it means less capacity is actually going in. If it comes with noticeable heat or a swollen case, that is a safety issue, and the battery should be retired whatever capacity remains. Do not give it one last outing.
By contrast, a battery whose capacity has dropped but which charges and discharges normally with an intact case can still handle light duty, such as indoor setups or short time-lapse work. There is no need to rush.
Why this tier should be replaced earlier
The 750mAh is the smallest of the three tiers in this LP-E17 range and is positioned as a light spare rather than a primary. That position gives it less tolerance for degradation: a 950mAh at 80% still holds about 760mAh, enough for a short shoot, while a 750mAh at 80% holds only 600mAh, and a margin that was already narrow becomes tight immediately.
So bring the replacement threshold forward for this tier: at around 70% it can move to the second string. If you find yourself relying on it to rescue more and more shoots, the problem is not aging but an undersized primary. Look at the 950mAh version, or rework the setup against the capacity and compatibility guide.
FAQ
Will a 750mAh definitely drop to 80% after a year?
Not necessarily. The 80% figure corresponds to the 300 to 500 cycle rule of thumb, and the real outcome depends on charging frequency, storage temperature and depth of discharge. A battery used once a week and stored at room temperature may still be above 90% after a year, while one shot daily and always run to shutdown can reasonably be at 80% in the same time.
Does running the battery to shutdown speed up the fade?
Yes. Deep discharge puts more structural stress on the anode, and repeated over time it fades faster. A safer habit is to swap at around one bar rather than let the body force a shutdown every time. Lithium-ion batteries have no memory effect, so partial charging is gentler.
How do I tell whether the battery or the body is at fault?
Cross-check. Fit the 750mAh into another compatible body, and fit a known-good battery into the original body. If the fault travels with the battery, the battery is at fault; if a fresh battery makes the original body behave, the fault may lie in the body contacts or power management. With the LP-E17 covering so many bodies, borrowing one to compare is usually easy.
Can a battery at 70% still serve as a spare?
Yes, with lower expectations. Keep it at the bottom of the bag as the last battery, not one you plan to use. Also avoid leaving it flat for long periods, which accelerates further loss; the storage advice in the LP-E17 overview covers this.