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What size SLA battery do I need?
12:11PM 9th Sep 13

What size SLA battery do I need?

“I don’t want to run my sounder battery flat, what size do I need?”

Key points:

• Do not flatten SLA batteries more than 50% for best performance
• Always fully recharge SLA batteries as soon as possible
• Always keep SLA batteries “topped up” when not in regular use
• Valve regulated lead acid batteries are commonly referred to as SLA batteries
• There are two interchangeable types: AGM and Gel batteries

Summary:

SLA batteries are an excellent means of powering electronics and other accessories on kayaks, especially as they won’t leak if tipped upside-down. They perform best and last longest if not routinely discharged more than 50%, followed by an immediate and complete recharge. This makes it important to select the right size battery for your sounder. Remember, using a battery that’s too small will compromise its performance and life expectancy. The only difficulty with using a battery that’s too large is a little extra weight – performance will be excellent.

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Here are three examples showing how to calculate the size of battery needed for different electronics. The idea is to keep from running your battery flat during a normal day on the water and reducing its life expectancy. Remember to always completely recharge your battery(s) as soon as possible.

Example 1: Lowrance Elite 4X colour sounder, average fishing trip duration of 6 hours

• From published specifications the sounder is rated 0.25 amps.
• Multiply this by 6 hours on the water: 0.25A x 6hours = 1.5Ah (amp hours) used.
• Since we don’t want to use more than 50% of the battery capacity we need to double the amount we’ve used: 1.5Ah x 2 = 3Ah as the minimum battery size.
Most kayakers will choose the economical 7Ah battery because they’re common and relatively inexpensive. They also have the advantage of allowing occasional weekend trips without needing to be charged between sessions on the water (first day 1.5Ah used + second day 1.5Ah used = 3Ah for the weekend – still less than half the full 7Ah capacity of the battery). Just make sure the battery goes on the charger as soon as possible.

Example 2: Garmin Echo 300C colour sounder, average fishing trip duration of 6 hours

• From published specifications the sounder is rated at 1.0 amp.
• Multiply this by 6 hours on the water: 1.0A x 6hours = 6.0Ah (amp hours) used.
• Since we don’t want to use more than 50% of the battery capacity we need to double the amount we’ve used: 6.0Ah x 2 = 12Ah as the minimum battery size.
This shows how one size doesn’t fit all when it comes to selecting batteries for sounders. This unit ideally needs to be matched with a single 12Ah battery for day trips, or 2x 7Ah batteries connected in parallel (positive-to-positive, negative-to-negative) giving a total of 14Ah capacity. Weekend trips are always going to run the battery(s) too flat unless they’re charged between sessions.

Example 3: Lowrance Elite 7 HDI Sounder GPS Plotter, average fishing trip duration 8 hours

• From published specifications the sounder is rated at 0.75 amps.
• Multiply this by 8 hours on the water: 0.75A x 8hours = 6.0Ah (amp hours) used.
• Since we don’t want to use more than 50% of the battery capacity we need to double the amount we’ve used: 6.0Ah x 2 = 12Ah as the minimum battery size.
This shows how a large 7’ screen high performance sounder with a modest current rating doesn’t necessarily need a huge battery, even if your typical session on the water lasts all day.

In summary:

SLA batteries are an excellent means of powering electronics and other accessories on kayaks, especially as they won’t leak if tipped upside-down. They do have one characteristic that’s often misunderstood: they do not like being run flat and will perform best if constantly kept fully charged. This makes it critical to purchase a SLA battery that’s large enough to supply your power needs for the day and not use more than 50% of its capacity. It’s also critical to recharge a SLA battery as soon as possible, even if it’s only been used for a short period.

Looking for a new sounder but can’t decide which way to go? Want to find out which battery is best suited to your sounder, GPS, or Chart Plotter? Get in touch with local Viking Kayaks fishing specialist Stephen Tapp for more advice.

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