Who this is for: you run a private LN node on your phone (Zeus, Blixt, Lightning Pub...) and you keep an onchain "cache / buffer" of sats on your desktop. Your SPEND wallet (mobile node) ran dry paying for stuff, and you need to move sats back into its channels so you can keep spending.

What we'll build: Electrum becomes your refill pump. It holds your onchain cache + one Lightning channel of its own, and its built-in submarine swaps move sats between the two without Boltz and without opening/closing channels. Then you pay your mobile wallet's invoice from that channel. Repeat as needed.

How it works (the 2-minute mental model)How it works (the 2-minute mental model)

1. You keep a buffer of onchain sats in Electrum (your CACHE wallet).
2. You open one Lightning channel in Electrum (trampoline or regular).
3. When your mobile SPEND wallet empties, you pay its Lightning invoice from Electrum's channel: sats land in your phone wallet in seconds.
4. When Electrum's channel empties, you top it back up from Electrum's onchain balance using its integrated submarine swap. No new channel, no Boltz.
5. Repeat forever.

PrerequisitesPrerequisites

• Electrum 4.6 or newer (4.8 is current as of this writing). Download from electrum.org and verify the GPG signature before running it.
• A wallet with native SegWit (bc1) addresses and a software keystore (an Electrum seed). Since 4.6, channels use anchor commitments, which require a software keystore: hardware-wallet-only and watching-only wallets can't open channels.^[1]
• An onchain balance in that wallet (your cache buffer). Fund it from your exchange, cold storage, or cache wallet.
• Back up your wallet file and seed before you touch channels.

Step 1: Enable Lightning in ElectrumStep 1: Enable Lightning in Electrum

Open your wallet, then go to the Channels tab. If Lightning isn't active yet, Electrum will ask you to activate it. You can also check under Tools → Preferences → Lightning.

Useful Preferences while you're there:

• General → Base unit: switch to sats (or keep BTC and just be careful with zeros).
• Transactions: enable RBF and spend only confirmed coins if you like extra care with UTXO management.

Step 2: Deposit your onchain bufferStep 2: Deposit your onchain buffer

• Go to the Receive tab, generate a new address, and label it (right-click → Edit label) so you know what it's for.
• Send your cache sats there from wherever your buffer lives (exchange / cold wallet / cache wallet).
• Wait for at least 1 confirmation before opening a channel; for big amounts wait for 3-6 to be safe.

Step 3: Open a Lightning channelStep 3: Open a Lightning channel

• Channels tab → New Channel.
• Amount: minimum is 0.002 BTC (200,000 sats) + miner fee. That's a small channel; if Electrum is going to be your recurring refill pump, consider a bigger one (500k–1M sats) so you don't have to repeat the onchain fee as often.
• Peer: two modes:
  • Trampoline mode (default, easiest): with Trampoline Routing enabled, Electrum only opens channels with its hardcoded trampoline nodes (ACINQ, Electrum's own node, Hodlister). Just click Suggest peer.^[2]
  • Regular mode: Tools → Preferences → Lightning → untick "Use trampoline routing", then paste the node URI of a peer you choose (a friend's public node, a well-known node, etc.). Electrum will download gossip and pick a suitable route.
• Wait for the funding transaction to confirm. Channel status becomes OPEN.

Trampoline vs regular channels: both work for this. Trampoline is simpler and good for beginners. With trampoline channels you also don't have to worry about spending/emptying them to be able to receive.

Step 4: Refill your SPEND wallet (mobile node)Step 4: Refill your SPEND wallet (mobile node)

This is the actual refill step, and it's just a Lightning payment:

1. On your mobile wallet (Zeus/Blixt/Lightning Pub...), tap Receive, create an invoice for the amount you want to refill (e.g. 300,000 sats). Add a small buffer for routing fees.
2. In Electrum: Send tab → paste the invoice → make sure the payment comes from Lightning (Electrum will show "send onchain" vs lightning options; for a bolt11 invoice it pays over LN automatically) → confirm.
3. Sats arrive in your mobile wallet in a couple of seconds. Its channel now has outbound liquidity again: your SPEND wallet is refilled.

Step 5: Top the Electrum channel back up (the refill pump)Step 5: Top the Electrum channel back up (the refill pump)

Once Electrum's own channel is low, refill it from its onchain balance without opening a new channel:

1. Channels tab → click the Submarine Swaps button (top-right, the two-arrows icon).
2. In the swap dialog, choose the direction onchain → Lightning (this is the "fund / receive into lightning" side of the dialog: toggle it off "swap to onchain").
3. Enter the amount and pick a fee rate. Electrum discovers swap providers over Nostr and shows you their fees: pick one, confirm.
4. Keep Electrum running until the swap is marked complete. You're moving sats from your onchain cache into your LN channel, trustlessly, with no third party holding funds.^[3]

Step 6: RepeatStep 6: Repeat

Every time the mobile wallet drains: pay its invoice from Electrum → top Electrum's channel up from onchain → repeat. Electrum stays at your desk as your always-available buffer.

The reverse direction (freeing inbound / pulling sats out)The reverse direction (freeing inbound / pulling sats out)

Two handy extras that round out Electrum as a liquidity tool:

• LN → onchain (to empty a channel, free inbound liquidity, or move sats to cold storage): same Submarine Swaps dialog, other direction. Since Electrum 4.7 you can also just use the Send tab → Submarine Payments to pay an onchain address directly from your Lightning balance.^[4]
• Fee tip for swaps when you're not in a hurry: use the Static / slow option at 10–15 sats/vB (or lower) and wait. The swap confirms when the mempool clears.

Gotchas & notesGotchas & notes

• Keep Electrum running during any swap. Closing the app mid-swap can stall it.
• Anchor channels always need onchain UTXOs available in the wallet (that's part of the anchor commitment design). Keep a little onchain balance around: which you're doing anyway.
• Since Electrum 4.6, zero-conf swaps are gone: swaps confirm onchain first. Don't panic if the swap sits "pending" for a few minutes.
• Swap providers are discovered over Nostr; if the dialog shows no providers, check your connection/Nostr relay settings and retry.
• Known quirk: reverse swaps (LN → onchain) need Trampoline Routing enabled (Tools → Preferences → Lightning). If you get "insufficient outgoing capacity" errors with plenty of balance, that's the cause: enable trampoline and restart.
• Don't use a hardware-wallet-only wallet for channels (anchor commitments need the software keystore).
• Channels opened in Electrum can be force-closed from your seed alone if you ever lose the wallet file: the seed is the real backup.

Cost check (rough, mainnet, 2026)Cost check (rough, mainnet, 2026)

• Opening the channel: one onchain miner fee (plus the ~200k sats you lock in the channel).
• Swap onchain → LN: onchain miner fee + a provider fee (typically a few tenths of a percent, shown before you confirm).
• Swap LN → onchain: onchain miner fee + provider fee.
• Paying your mobile wallet over LN: normal routing fees (usually a few sats + a fraction of a %).
• No Boltz, no exchange, no new channel per refill.

Note: This guide may contain inaccurate information as technology evolve and tooling tune up. Feel free to report any inaccurancy in the comments below.

1. "Anchor commitments" are channel updates that let Electrum bump the fee of an unconfirmed channel transaction by spending an anchor UTXO: that's why Electrum needs a software keystore to sign, and why hardware-only and watching-only wallets can't hold channels. See the Electrum release notes. ↩

2. With trampoline routing, Electrum opens channels only with its bundled trampoline nodes (ACINQ, Electrum's own node, Hodlister) and routes payments through them: no need to manage gossip or pick peers yourself. ↩

3. Swap providers are discovered over Nostr; each one's fees are listed in the dialog before you pick one. See Electrum docs: Submarine swaps. ↩

4. Submarine Payments (Electrum 4.7+) let you pay an onchain address directly from your Lightning balance, without the swap dialog. See the Electrum release notes. ↩