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Modern twist on old battery type cuts aircraft maintenance hours, costs

by Robert Kaper
NAVAIR Public Affairs Office

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A program to replace troublesome nickel-cadmium batteries with a modern version of old-fashioned lead-acid cells in some Navy aircraft is expected to save $1.5 million annually in replacement costs and nearly 56,000 hours in maintenance, according to the Power and Energy Division of NAVAIR Propulsion and Power Department, Air 4.4.

The investment required to reap those benefits every year was a one-time grand total of $205,000 from NAVAIR and the Defense Logistics Agency, said Bill Johnson, Electrical Power Systems branch manager at NAS Patuxent River.

That’s how much it cost to flight-qualify the new valve-regulated, lead-acid (VRLA) batteries as a replacement for the once-standard, nickel-cadmium (NiCd) batteries.

The first aircraft in the current group getting the replacements – the H-53 heavy-lift helicopters – are already saving the Navy $761,000 annually in consumable costs for new batteries and over 31,000 hours in maintenance.

The next expected savings increment – over $700,000 in consumables and 24,000 hours in maintenance – will come from EA-6B Prowlers, which began swapping their NiCds for VRLAs last June.

Next in line for VRLA batteries is a small number of F-5E/F aggressor aircraft. The aircraft may be best known for playing a part in Top Gun combat training as “the enemy.” The change is expected to save nearly $52,000 in consumables and 67 hours in maintenance savings annually.

The NiCd batteries provided power for critical auxiliary systems, such as fire suppression and emergency egress lighting on H-53s, and the EA-6B’s inertial navigation system and spin-assist airbrakes. In addition, many of the batteries had to power such critical systems as flight-control computers when the main engine-driven generator power failed.

“We say these batteries are ‘your last chance for romance’,” Johnson said. “Otherwise you’re swimming with the sharks.”

NiCds originally were chosen for their high power and supposed low maintenance. But on the H-53 their service life was shorter than expected, and maintenance costs were high.

“One out of 12 failed every month because of poor design,” said Johnson, “That means that we had to replace all of them after a year.”

The NiCd batteries would self-discharge when not being used. Some also suffered from a “memory effect” that kept them from being fully recharged. If NiCds are discharged repeatedly to the same level, they tend to “remember” that level and can’t be brought back to full capacity.

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“The maximum level keeps dropping at each recharge,” Johnson said. “Eventually you have to short it out and start all over again.” That need for frequent restarts was the reason that NiCds had such high maintenance requirements.

Those problems haven’t surfaced in the new VRLA batteries. None have failed so far, and they don’t require any scheduled maintenance.

“To be conservative, we replace them every three years because of possible lead fatigue,” Johnson said, “but they come off the plane with the same capacity as when they went on.”

The new VRLA batteries themselves are 33-50 percent cheaper than NiCds, leading to a corresponding reduction in the cost of consumables. An equivalent savings also comes from the dramatic reductions in maintenance.

Maintenance on NiCd batteries in the H-53E fleet, for example, approached 37,000 hours a year. For the new VLRA batteries, that time is approximately 5,500 hours a year.

The only maintenance required on the new batteries is the occasional need to pull one for a recharge when it runs down, explained Johnson.

“The battery could be run down when if an aircraft sat for a long time with a background load that kept important codes alive in computer memory, or if an aircraft system was inadvertently left on,” he said.

The dependable lead-and-sulfuric-acid chemistry in VRLA batteries has been around for more than a century. It’s also used in car batteries. To make it suitable for aircraft, VRLA batteries incorporate a few modern wrinkles.

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No maintenance needed on VRLA battery (right) with lid securely riveted shut. Troublesome NiCd battery on left. US Navy photo.

VRLAs are completely sealed with no vent openings, and the acid inside them is absorbed by porous fiberglass mats between the plates, so VRLA batteries are often referred to as Absorbed Glass Mat – AGM – batteries.

The liquid acid in a car battery pours out of the vent openings if it’s turned upside down, which is not good in an airplane.

A car battery needs vent openings to release the hydrogen gas that forms while charging. But a VRLA battery absorbs hydrogen internally as it’s charged, eliminating the need for vents. If something goes wrong with hydrogen absorption, a valve opens to let the gas escape (valve regulation) so the battery doesn’t explode.

By updating tried-and-true chemistry with modern technology, the valve-regulated, lead-acid battery has given this 19th-century invention a new lease on life and saved the Navy a significant amount of money in the bargain.

¬Photo cutlines

CH-53E Sea Stallion lowers swimmer during helo-cast. New VRLA batteries in H-53s save $761,000 in replacement costs and over 31,000 maintenance hours each year. US Navy photo.

E/A-6B Prowler deploys spin-assist airbrakes on wingtips during touch and go. Batteries operate these critical components if main engine-driven generator power goes down. US Navy photo.

Source: NAVAIR