12V 46Ah Lithium Battery: Max Capacity in a Group U1 Case

Short answer: The Pro-Guide PGLM46 is a 12V 46Ah lithium battery (LiFePO4) that packs 588 watt-hours into a standard Group U1 case (7.64 x 5.20 x 6.81 in) and weighs only 10.14 lb. It is the highest-capacity battery in Pro-Guide's U1 lithium line, rated for more than 3,000 cycles at 80% depth of discharge, accepts up to a 46A charge, and carries a 5-year free replacement and 10-year pro-rata warranty.

If you already own a U1 sealed lead-acid or AGM battery, you know the trade-off: it is heavy for its size, you can only use about half of its rated capacity, and it rarely lasts more than a few seasons. This guide is about swapping that battery for the most capacity a U1 case can give you. We cover what 46Ah of lithium really means in runtime, how it compares with a U1 AGM, a step-by-step swap checklist, charging, and when the PGLM46 is the better pick than the 35Ah PGLM35 or the 50Ah PGLM50.

Key Takeaways

• Most capacity per U1 case: 46Ah and 588Wh, the largest of Pro-Guide's Group U1 lithium batteries.
• Light for its size: 10.14 lb (4.6 kg), with a built-in carry handle.
• Runtime: about 23 hours on a 2A fish finder and about 4.6 hours on a 10A load.
• Fast charging: 10A standard and 46A maximum charge current, roughly 1 hour from empty at the maximum.
• Built to last: more than 3,000 cycles at 80% depth of discharge, backed by a 5-year free replacement and 10-year pro-rata warranty.

What Does a 12V 46Ah Lithium Battery Give You?

Amp-hours (Ah) measure how much current a battery can deliver over time. A 46Ah battery can, in theory, supply 1 amp for 46 hours, 2 amps for 23 hours or 10 amps for 4.6 hours. The PGLM46 is labeled 12.8V nominal, and 46Ah at that voltage works out to the 588 watt-hours Pro-Guide lists for it.

What makes 46Ah of lithium different from 46Ah of lead-acid is how much you can actually use. Lead-acid and AGM batteries are usually discharged only about halfway to protect their life, so a lead-acid battery's practical capacity is roughly half its label. A LiFePO4 battery like the PGLM46 can use nearly all of its rated capacity while holding steady voltage. In practice, that means the PGLM46 gives you far more usable energy than a typical U1 lead-acid battery in the same space.

The PGLM46 is a deep cycle battery, built for steady power over hours. Its label notes that it is not designed for engine starting.

Pro-Guide PGLM46 Specifications

Model / SKU	Pro-Guide PGLM46
Group size	U1
Chemistry	Lithium iron phosphate (LiFePO4), deep cycle
Voltage	12V (12.8V nominal on the label)
Capacity / energy	46Ah / 588Wh
Cycle life	More than 3,000 cycles at 80% depth of discharge
Charge current	10A standard, 46A maximum
Terminals	Internal thread (M6)
Protection	Built-in battery management system (BMS)
Bluetooth	Enabled
Dimensions	7.64 x 5.20 x 6.81 in (194 x 132 x 173 mm)
Weight	10.14 lb (4.6 kg)
Warranty	60-month free replacement, 120-month total pro-rata

Charging rules from the battery's top label are in the charging section below.

The PGLM46 puts 46Ah and 588Wh in a standard Group U1 case at 10.14 lb.

How Long Will a 12V 46Ah Lithium Battery Last?

Divide 46Ah by your load in amps for a rough estimate. Add up everything on the battery, and check your equipment manuals for the actual draw.

Load	Draw	Estimated runtime on the PGLM46
Single fish finder	About 2A	About 23 hours
Two graphs plus accessories	About 5A	About 9 hours
Larger electronics load	About 10A	About 4.6 hours

These are estimates. Real runtime depends on the load, temperature and how far you discharge the battery. Pro-Guide's label warns not to discharge the PGLM46 below 12V, so recharge before it is completely flat.

The extra capacity over the 35Ah PGLM35 matters most when you fish two days between charges, run more than one graph, or simply want a buffer so you never think about the battery during a long day.

46Ah Lithium vs. a U1 AGM or SLA Battery

Factor	Pro-Guide PGLM46 (LiFePO4)	Typical U1 AGM / SLA
Usable capacity	Nearly all of 46Ah	About half of the rated capacity
Weight	10.14 lb	Typically about twice as heavy or more
Cycle life	More than 3,000 at 80% DoD	Typically a few hundred cycles
Voltage under load	Steady until nearly empty	Drops steadily as it discharges
Charge time	About 1 hour at the 46A maximum	Usually many hours
Warranty	5-year free replacement, 10-year pro-rata	Usually 1 to 2 years

Here is a simple way to think about it: if your U1 lead-acid battery is rated somewhere in the 30s of amp-hours, you are probably using about half of that on a good day. The PGLM46 gives you nearly all of 46Ah, at a fraction of the weight, and keeps doing it for thousands of cycles instead of a few hundred.

What Is the PGLM46 Best For?

• Multi-graph electronics setups: a dedicated U1 battery for your fish finders isolates sonar from motor and engine noise. See Should You Run a Separate Battery for Your Boat Electronics?
• Kayaks and small boats with a U1 box: more runtime without changing the box.
• Multi-day trips: camping, overnight fishing and anywhere charging is not available every night.
• Light RV and solar storage: 588Wh for lights, fans and device charging.
• Other U1 deep cycle uses: one customer reported using the PGLM46 in a mobility scooter in place of its sealed lead-acid batteries and said the fit was perfect. If you are considering a non-marine use, check your equipment maker's requirements and call our team first.

The PGLM46's top label includes a quick voltage guide: about 13.8V at 100% and 13.0V at 20% charge.

How to Charge the PGLM46

Charge time is roughly the capacity divided by the charger output:

• 10A standard: about 4.6 hours from empty, for example with the Pro-Guide 12V 10A 1-Bank Battery Charger on its 12V lithium profile.
• 30A: about 1.5 hours from empty with the Pro-Guide 12V 30A Lithium Battery Charger.
• 46A maximum: about 1 hour from empty.

Follow the rules printed on the battery label:

1. Use a smart lithium charger and keep charging voltage between 14V and 15V. Below 14V it cannot be fully charged; above 15V it will be overcharged.
2. Skip desulfation mode. Automatic desulfation is for lead-acid batteries and should not be used.
3. Don't discharge below 12V. The label warns this may damage the battery.
4. Read voltage after resting. Wait 1 to 2 hours after charging. About 13.8V means full; about 13.0V means it is at roughly 20% and due for a charge.

As with all LiFePO4 batteries, charge in moderate temperatures and avoid charging below freezing.

Swapping a U1 Lead-Acid Battery for the PGLM46

1. Check the job

The PGLM46 is a deep cycle battery. If your old U1 starts an engine, it is the wrong replacement.

2. Check the charger

This is the step people miss. A lead-acid charger may not charge lithium fully, and one with an automatic desulfation mode should not be used at all. Make sure your charger has a LiFePO4 or lithium profile in the 14V to 15V range.

3. Check fit and terminals

The PGLM46 uses the standard U1 case, but measure the height and the clearance above the terminals. It has internal-thread M6 terminals, so you may need new M6 bolts or ring terminals. A NOCO Group U1 Snap-Top Battery Box keeps it secured and the terminals covered.

4. Fuse and secure

Install a fuse or breaker close to the battery on the positive cable, and strap the battery down so it cannot shift.

5. Mind the multi-battery limits

If your equipment uses more than one battery, use matching batteries at the same state of charge and stay within the label limit of no more than 4 batteries in series or parallel.

6. Monitor it

Bluetooth is listed as enabled on the PGLM46, and the product page links to the Pro-Guide Power iOS app for checking the battery.

PGLM46 vs. PGLM35 and PGLM50

Spec	PGLM35	PGLM46	PGLM50
Capacity / energy	35Ah / 448Wh	46Ah / 588Wh	50Ah / 640Wh
Case	Group U1	Group U1	Non-standard, 7.75 x 6.5 x 6.9 in
Weight	9.48 lb	10.14 lb	14 lb
Charge current (standard / max)	10A / 35A	10A / 46A	10A / 50A

Choose the PGLM35 if you want a lighter U1 and a day of runtime is plenty. Choose the PGLM46 for the most capacity that still fits a standard U1 box. Choose the PGLM50 if you do not need the U1 footprint and want 50Ah with a published 50A continuous discharge rating and IP65 case, for example for forward-facing sonar or a kayak trolling motor.

Frequently Asked Questions

How long will a 12V 46Ah lithium battery last on a fish finder?

Divide 46Ah by the draw. The Pro-Guide PGLM46 runs a 2A fish finder for about 23 hours and a 10A electronics load for about 4.6 hours. Actual runtime varies with load and temperature.

Is the PGLM46 a Group U1 battery?

Yes. The PGLM46 uses a Group U1 case measuring 7.64 x 5.20 x 6.81 in (194 x 132 x 173 mm). Check height and terminal clearance before installing.

How much does the PGLM46 weigh?

The PGLM46 weighs 10.14 lb (4.6 kg), much lighter than a typical U1 lead-acid or AGM battery.

How long does the PGLM46 take to charge?

About 4.6 hours from empty at the 10A standard charge current, or about 1 hour at the 46A maximum. Use a charger with a LiFePO4 profile.

Can I use my old lead-acid charger with the PGLM46?

Only if it has a lithium (LiFePO4) profile in the 14V to 15V range and no automatic desulfation mode. Otherwise use a lithium-compatible charger.

What is the difference between the PGLM46 and PGLM35?

Both use the same Group U1 case. The PGLM46 holds 46Ah (588Wh) and weighs 10.14 lb; the PGLM35 holds 35Ah (448Wh) and weighs 9.48 lb.

What warranty comes with the PGLM46?

A 60-month (5-year) free replacement warranty and 120 months (10 years) of total pro-rata coverage.

Get the Most Out of Your U1 Space

If you want the most runtime a Group U1 case can hold, the Pro-Guide PGLM46 delivers 46Ah and 588Wh of LiFePO4 power at 10.14 lb, with more than 3,000 cycles of life and a 10-year warranty. It is the simplest way to retire a heavy U1 lead-acid battery for good.

SHOP THE PRO-GUIDE PGLM46

Questions about swapping your U1 battery? Call our team at 1-800-827-3232 or browse all deep cycle lithium batteries and chargers.

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