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Can the $60 IDX SL-F50 L-Series Battery Compete Against the $120 Sony NP-F970?

If in the market for Sony L-Series batteries, there are a half dozen brands from which to choose. Sony sells their premium NP-F970 for a premium price of $120 while Anton Bauer, GVM, and, of course, Watson* undercut that price with their own budget models. How they achieve the same capacity at a third the price is a mystery. Are they using lower quality cells and cheaper plastic? How does the quality control compare to that of Sony? When buying budget, the unease from these questions is part of the payment.

And then there is IDX System Technology, a brand that I only just heard about from rave reviews on a Facebook group for Z Cam users. On there, they praised the price, performance, and ports of the brand’s SL-F50 and SL-F70 Sony L-Series batteries.

*But in the camera world, Sherlock’s sidekick wears a moth-eaten tweed jacket and shows two out of the four times you call him to the scene.

Specs

Spec wise, the IDX System Technology SL-F50 matches the form factor of the Sony NP-F970 while including USB and X-Tap ports and packing increased energy capacity at half the cost. The battery also weighs 18% less than the Sony and does what no L-Series from Sony has yet to do: indicate the battery level on the front.

For all the extra features, IDX’s new battery does not just exist as another budget option. There are legitimate benefits, such as powering a motorized follow focus with the USB port while running a monitor.

Sony NP-F970IDX SL-F50
Price$120$60
Capacity45 Wh48 Wh
Amp-Hours6300 mAh6600 mAh
Weight304g250 g

But are these extra features too good to be true? Wanting to find out, I bought one and began testing it.

On first sight of the SL-F50, I had a little suspicion about its actual energy capacity given the way the deep USB port on the top prevents the inclusion of a third row of 18650 battery cells. Rather than six cells, it can hold up to four cells.

IDX must be using four newer, more efficient, and higher capacity cells to accomplish the job of Sony’s six older cells. The reduced weight and greater energy capacity of this battery are strong indicators of fewer and newer cells.*

The totally unscientific test I ran during a pandemic level of patience certainly strengthens this thought.

*Later when checking out the IDX site, I found them mentioning exactly this: “IDX excels in combining high watt-hour capacity with low physical weight.”

Sony vs IDX Battery Life

Over two days, I ran a SmallHD 702 Touch monitor at 100% brightness on both an IDX SL-F50 and Sony NP-F970. At roughly the same room temperature and starting monitor temperature, I ran both batteries from off-the-charger full to empty. For each battery, I recorded a time-lapse of the voltage indicator on the monitor. The monitor was hooked up via HDMI to a powered Z Cam S6 for the whole test.

Photos for the time-lapse were taken in 10-second intervals. I determined the total time duration of each battery by relying on the number of photos taken before the monitor went black.

BatteryTotal photosTotal time
Sony NP-F970949 photos2 hours 38 minutes
IDX SL-F50969 photos2 hours 41 minutes

The NP-F970 lasted for two hours and thirty-eight minutes. The IDX battery squeaked by the Sony with three extra minutes of run time for a total of two hours and forty-one minutes before the monitor went black.

IDX is clearly not lying about the energy capacity in this battery. The cells inside the SL-F50 have more energy than the cells in the NP-F970, and by doing so they require fewer batteries to achieve the same runtime. Fewer batteries also means more room for those USB and X-Tap ports and the battery indicator.

Discharge Profile

For the technical minded, I used the photos from the time-lapse to determine the discharge profile of each battery.

The SmallHD 702 Touch indicates the voltage of the battery with a resolution of 0.1 volts, though unsteadily in that it begins to switch erratically between the lower and higher voltage, such as 7.9v and 7.8v, when near the lower one. The timing of when the voltage decreased by 0.1 was chosen based on the first instance of the reduced voltage on the monitor.

Unfortunately, the monitor switches the indicator to “LOW” once a battery drops below 6.8 volts. Both batteries lasted about forty-five minutes after the indicator had gone to “LOW,” and it was in those forty-five minutes that the IDX battery rose up and beat the Sony battery.

From what could be seen, the discharge profile of the Sony NP-F970 is not linear. The voltage decreased at twice the rate of the IDX SL-F50 for the first ten minutes before leveling off to a steading drip. The SL-F50 remained nearly linear for the visible duration.

Conclusion

IDX System Technology’s SL-F50 is more than a budget battery the likes of Watson and GVM. With greater capacity, USB and X-Tap ports, lighter weight, and a battery indicator all wrapped up in a price that is exactly half that of Sony’s battery, The SL-F50 is definitely worth considering over the competitors when looking to buy new Sony L-Series batteries.

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